Aromatic Sulphonation and Related Reactions · Aromatic Sulphonation and Related Reactions the...

Aromatic Sulphonation and Related Reactions


Soile, Olutola O. Bob*1 , Oyeyiola ,Felix Adetunji

1 and Avan ,Erhunmwunsee Dalton

2

1Department of Chemistry and Biochemistry, Caleb University, Imota. Lagos,Nigeria.

2Institute for Human Resources Development,Mamuko Campus,Federal University of Agriculture,Abeokuta,Nigeria.

*Corresponding author. [email protected], 234-802 310 7681.

SUMMARY

Aromatic sulphonation and related reactions are of immense importance industrially having wide application in

dyestuff and pharmaceutical industries, as well as in tonnage chemical production such as in the manufacture of

detergents. Consequently, much of the published work on this subject comes from industrial laboratories, often as

patent specifications.

. This survey covers the direct sulphonation of benzene and many of its derivative, of naphthalene and of the simpler

aromatic heterocycles. Sections are also devoted to the topics of chlorosulphonation and sulphone formation, with a

brief mention of desulphonation.

The“related reactions” have been taken as those reactions which occur concurrently with sulphonation. These include

desulphonation and sulphone formation. Also chlorosulphonation has been considered, as often the sulphonic acid is

not isolated, being immediately converted to the sulphonyl chloride.

Keywords: Aromatic sulphonation , desulphonation ,sulphone , chlorosulphonation

Introduction

Aromantic sulphonation is an organic reaction in which in which a hydrogen atom on an aromatic molecule is replaced

by a sulphonic acid functional group in an electrophillic aromatic reaction.

There are a variety of reagents which are commonly used to introduce the – SO3H group into an aromatic molecule, the

most widely used being sulphur trioxide, oleum , sulphuric acid, chlorosulphonic acid complexes of sulphur trioxide.

It is useful to regard this simply as donors of sulphur trioxide.

The choice of sulphonating agent is important as in general ,side reactions such as sulphone formation, rearrangement,

and anhydride formation increases with increasing reaction temperature and sulphur trioxide content.

The properties of the various reagents are discussed in other literature 1-10. A comparative study of the sulphonation of

1,3,5, and 1,3,7 trichlorosulphonyl naphthalene at 150-1700c, and 1,5 dichloulphonyl naphthalene at 1000c showed that

the order of activity of the sulphonating agents was 55% Oleum > 73% Oleum > SO3> ClSO3H > H2SO4 11

The fact that oleum appears to be more reactive than sulphur trioxide is attributable to a solvation effect. Complexes of

sulphur trioxide were not studied but presumably would have been much less reactive than sulphur trioxide. These

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complexes have been well reviewed 2,11 and most of the work with complexes has been in the in the sulphonation of

heterocyclic compounds, some of which may be sulphonated using sulphuric acid or oleum, but better yields are often

obtained using these much milder complexes.

Mechanism

The mechanistic studies that have been carried out on sulphonations have usually been done on simple aromatic

hydrocarbons. The conclusions from these investigations are summarized below. Mechanistic features of the

sulphonation of heterocycles and ionic compounds such as phenols are given later.

Kort and Cerfontain 5 investigated the homogenous sulphonation of chlorobenzene in aqueous sulphuric acid and they

found a marked decrease in the substrate kinetic isotope effect on the acid concentration was increased from 95 to 97;,

the reaction rate also increased. This could be interpreted by a mechanism involving attack by sulphur trioxide

(perhaps solvated) to form a σ complex, typical of other electrophillic aromatic substitutions, followed by the base

assisted removal of a proton (This is partly rate determining at high acid concentrations).

Cl Cl

SO3H H

+ SO3

(or SO3H2SO4)

ArSO3H + H2SO4

This is in agreement with earlier work on oleum, which proposed stepwise attachment of sulphur trioxide and a

proton followed by the loss of a proton from the benzene ring6, 12. A similar mechanism is indicated when

sulphur trioxide (in low concentrations) is used as the sulphonating agent. Thus Walsh and Davenport13 used

SO3. dioxan complex in excess of dioxan to sulphonate anisole, and obtained the rate expression.

-d[SO3] = K [ArH] [SO3] [HX]0 dt Where the term [HX]0 denotes the sum of the concentrations of all the proton donating species present, and was a

constant for any given run.

This expression was explained by the fast addition of sulphur trioxide followed by a slow protonation and base assisted

hydrogen abstraction. Further evidence that sulphur trioxide attacks in this manner is given by the fact that the small

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kinetic isotope effect has been determined for the sulphonation of benzene with sulphur trioxide in nitromethane

solvent14.

In high strength oleum and larger sulphur trioxide concentrations, the sulphonation reaction becomes second order in

sulphur trioxide, and the reaction shows no kinetic isotope effect. It has been proposed that in these cases, Szo6 is the

attacking electrophile; this is a cyclic dinner of sulphur trioxide15. However, the kinetics are more usually interpreted as

due to the rapid addition of sulphur trioxide as before to give an intermediate which then rapidly reacts with another

molecule of sulphur trioxide16,17. This new intermediate may then rapidly abstract a proton from the ring yielding a

pyrosulphonate which then decomposes to the parent acid:

ArH + SO3 Ar Ar

H

SO3

H

SO2OSO3

SO3

SO3H

H

S

O

O

S

O

O

O O

The pyrosulphonic acid has never been isolated from the reaction mixture.

Sulphonations have proved to be extremely difficult to study kinetically because of the many competing reactions. In

the sulphonation of toluene, for example, oleum gives all three isomers of the monosulphonic acid, some

disulphonation, sulphone formation, anhydride formation and desulphonation as well as some breakdown of the

aromatic substrate. For these reasons, overall rate constants are of little use in elucidating mechanisms, and recently

there has been a tendency to calculate the partial rate factors for the positions on the aromatic ring. These give a useful

indication of substituent effects.

Workers have tended to use slightly deactivated substrates, such as chlorobenzene, for kinetic studies on sulphonations,

as these react slowly and smoothly to give little ortho or meta-sulphonation, and little desulphonation or sulphone

formation, and they are also stable to the strong reagents used.

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Sulphonation is an electrophyllic substitution reaction, and shows the same dependence of rate of reaction to

substituents as do most other electroplules. Thus alkyl groups and fluorine increase the rate of sulphonation in

benzene, other halogens decrease the rate, and the metro group deactivates the ring completely7. In fact nitro-aromatic

compounds have been used as solvents in kinetic studies 14,18. Rate constants have been determined for most substituted

benzenes, but unfortunately there has been no uniformity in reaction conditions or reagent strengths, and so no

comparisons are likely to be meaningful. There have, however, been sufficient rate constraints determined in

nitrobenzene at 400c using sulphonic acid to compile the following table (19).(Table 1).

Table 1

Compound Velocity constant k ×106, 400c

Naplthalene 116.7

Meta-xylene 78.7

Toluene 26.1

1 nitro naphthalene 17.1

4-chloro toluene 15.5

Benzene 10.6

Chlorobenzene 9.5

Bromobenzene 6.7

Meta-dichloro benezene 3.3

4-nitrotoluene 1.0

Para-dichlorobenzene 0.98

1,2,4 trichlorobenzene 0.73

Nitrobenzene 0.24

An early study(20) in the sulphonation of para nitro toleuene showed a large change in rate constant at 250c when the

reaction strength was varied between 99.4% acid to 2.4% oleum,the reaction being first order in aromatic concentration.

Forty years later, Cowdery and Davies 21 working between 92% acid and 10% oleum, showed that in oleum the reaction

obeyed the following rate equation.Rate = K [Aromatic] [SO3].

and they calculated the activation energy to be 18kcalmole-1. Kilpatrick et al22 investigated the sulphonation of benzene

in sulphuric acid and found that the reaction obeys the equation.Rate = K’ [Aromatic][H2SO4]2

aH20

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the appearance of the benzene sulphonic acid being followed by U.V absorption spectocopy. The same workers23 have

studied the sulphonation of mestylane in 12-13.5molar sulphuric acid at 12.30c, and found that simultaneous

sulphonation and desulphonation was occurring.

Kilpatrick and Meyer24 gave kinetic data for the sulphonation of toluene, ortho, meta- and para-xylenes, and 1,2,4 –

trimethyl benzene under conditions where the reaction goes to completion. Eaborn and Taylor25 have determined the

partial rate factors for the sulohonation of toluene with sulphuric acid containing tri fluoro acetic acid, they are f0 34, fm

42 and fp 112. In the same acid range at 250c, the partial rate factors for homogeneous sulphonation, have been

calculated to be f0 63.4, fm 5.7 and fp 25826. The homogeneous sulphonation of tert-butyl benzene in 86.3% sulphuric acid

at 250c gave partial rate factors calculated in fm 3.0 and fp 5327 . There was no otho-substitution. A comparison of the

partial rate factors for ortho-substitutions at 250c in 86.3% acid for toluene, ethyl benzene, isopropyl benzene and tert

butyl benzene showed the expcted decrease with increasing size of the alkyl group28.

Steric effects in the ortho position are also used to account for the difference in overall rate constants for the

homogeneous sulphnonations of toluene, ethyl benzene, and isopropyl benzene aat 250c in 75-95.9% sulphuric acid 29

First order rate constants have bveen calculated for the homogeneous sulphonation of benzene and toluene at 250c in

82.9% sulphuric acid30 and they were found to be

Kbenzene = 3.31 ± 0.06 × 10-6 sec-1

Ktoluence = 218 ±± 4 × 10-6 sec-1

The reaction rate was found to be first ordedr in aromatic hydrocarbon up to 98% conversion. Kort and Cerfontain 5

have determined the substrate isotope effect in the homogeneous sulphonation of chloro benzene at 250c with 83.4 –

99.6% sulphuric acid. Ko/KH varies from 0.8 in 95% acid to 0.4 in 97%.

In an important investigation into the sulphonation of several nitrated benzene derivatives, and halogenated benzenes,

with sulphur trioxide in nitrobenze, Hinshelwood et al31-33 found that the sulphonation reaction was second order with

respect to sulphur trioxide.Thi variation in kinetics between first order in sulphuric acd and second order in sulphur

trioxide indicates there are two competing mechanisms of sulphonation.

In another competitive study, Cerfortain and Telder 14 determined the kinetic isotope effect in the sulphnonation

benzenes with sulphur trioxide in nitrobenzene at 250c as KH/Ko = 1.35 ± 0.16; in MeNo2 KH/Ko = 1.25 ± 0.01.

There has only been one study 34 in a flow system using sulphur trioxide; the reaction with benzene was extremely

rapid and complex. The rate equation was too complex to be useful mechanistically.

Sulphonation of Benzene and derivatives

a. Benzene

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Benzene has been mono sulphonated using all of the more reactive sulphonating agents, such as oleum, sulphur

trioxide, sulphuric acid and chlorosulphonic acid. Disulphonation is not easily brought about, and the yield of the

monosulphunic acid is quite good. Thus a 97% yield is obtained using sulphur trioxide35 and a 90% yield using oleum36.

The disulphonation of benzene is much less facile, and a catalyst is usually necessary in order for a good yield to be

obtained. Reasonable yields were obtained by simply treating benzene with a large excess of 98% sulphuric acid 36; but

a yield of 94% was obtained using trioxide in the presence of a HgO catalyst 38.

b. Aromatic amines

These are thought to react by two different routes, depending on the acid concentration. Media of high sulphur trioxide

concentration, give the sulphonate, which can often be isolated. These then re-arrange to give the ortho-acid para-

sulphonic acids. Thus aniline -2- sulphonic acid is prepared by sulphonating aniline with S03- pyridine in the presence

of excess pyridine at 150-2000C39. Presumably the sulphonate first rearranges to the 4-acid, which then further,

rearranges under the reaction conditions to give the product.

Under less drastic conditions (i.e. below 800c) in the presence of excess acid or oleum, protonation of the amine occurs

giving a quarternary ammonium salt which is meta-directing with respects to elecrophillic reagents. Thus, sulphonation

of aniline gives a mixture of the 2-, 3- and 4- sulphonic acids, whereas N, N- dimethyl aniline gives a mixture of the 3-

and 4- acids40.

c. Phenols

As for anure, phenoes form sulphates with sulphur trioxide and other sulphonations. A study of the sulphonation of

phenol with chlorosulphonic acid lead to the following proposed mechanism.41.

PhOH + ClSO3H PhOSO3H + HCl

ClSO3H

HO3SC6H4OSO3HClSO3H + HOC6H4SO3HHCl

Since the activation energies for para-and other substitution only differ by 1.7 kcals mole-1 (para being the larger), both

isomers are formed in newly equal amounts.

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Phenols may be sulphonated with vigorous reagents and are amenable to the same techniques for increasing sulphonic

acid yield as for benzene. Thus the water produced in the reaction with 93% sulphuric acid has been azeotroped using

ethylene dichloride 42, but sulphur trioxide complexes give higher yields. Thus the sulphonation of para-

secalkylphenols with sulphuric acid gives 75% yield of the sulphuric acid, but with SO3- dioxan 90% yields were

obtained 43,44.

Careful choice of reagent and conditions make it possible to sulphonate one phenol selectively in a mixture. Thus

traces of phenol were removed from othochlorophenol containing less than 0.2% phenol 45.

Initially the sulphonic acid group is introduced ortho and para to the –OH group, but at high temperatures both

rearrange to give the thermodynamically more stable meta isomer. Thus the sulphonation of the ortho-cresol with

excess sulphuric acid gave only the para isomer at -100c, but at 150oc gave 87% of the meta sulphoric acid 46.

d. Halogen benzenes

Halogeno benzenes usually gives very little ortho-isomer in sulphonations, though both ortho-and para-isomers are

expected. This may be due to steric or inductive effects. Thus at 250c, 83.4-99.6% sulphuric acid gave 98.8% para, 0.8%

ortho acid 0.4% meta sulphonic acid on chloro benzene 4. Similarly, lodo benzene gave 98.3% para, 1.41% ortho acid and

0.3% meta sulphonic acid with sulphur trioxide in sulphur dioxide 47. However, prolonged heating of chlorobenezene

with 94% acid in a sealed tube at 185-2380c gives 54% meta and 46% parachlorobenezene –sulphonic acid. This is

another example of the para acid rearranging to the more stable meta acid 48.

e. Other derivatives

As would be predicted, nitrobeneze is very difficult to sulphonate, and liquid sulphur trioxide at 100-1500c is used

industrially, yielding almost entirely the meta-isomer 49. This reaction did not respond to iodine catalysis70.

Benzene acid gives the sulphonate with sulphur trioxide in dichloroethane51, but oleum gives mainly the meta-

sulphonic acid. However, iodine catalysis is reported to give a 95% yield of the ortho-sulphonic acid at 17.5 – 1900c 50.

Benzaldelyde is sensitive to oxidation, but oleum gives a reasonable yield of the meta sulphonic acid 52.

f. Toluene and xylenes

A great deal of work has been done on the sulphonation of toluene. Generally, all three isomers are produced with an

increase in temperature favouring the para and to a lesser extent the meta isomer, at the expense of the ortho isomer.

An increase in reagent strength decreases the para yield. Thus Spryskov and Gredin53 showed that the para yield

declined in the reagent series SO3, ClSO3H, H2SO4.

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By careful control of the reaction conditions, therefore, it is possible to obtain a high yield of the para-sulphonic acid.

Thus the sulphonation of toluene with sulphur trioxide in liquid sulphur dioxide gave 96.2% para isomer compared to

91.5% for the usual batch process. Carefully controlled conditions can also give an ortho yield of up to 50%, but for this

a vigorous reagent is needed, such as 98% acid, and this leads to much sulphone formation.

Vigorous conditions, such as high temperature and long reaction times lead to rearrangements via a desulphonation –

resulphonation reaction to give the meta-acid. Thus heating toluene -2, 4- disulphonic acid for 25 hours at 1970c gave a

65% yield of the more stable 3, 5 diacid 54.

The action of liquid sulphur dioxide to give such good yields of para-sulphonic acid with sulphur trioxide is not yet

clear, perhaps in some way the dioxide conplexes the trioxide, thus reducing its activity. The low temperature used (-

100c) is not sufficient to account for the great para-dominance. Isomer distributions using sulphur trioxide on tolueme

may shed light on thispoint, but as yet the data is not available.

The sulphonation of toluene is a heterogenous reaction, and apparently when sulphuric acid is used as the

sulphonating agent, most of the sulphonation occurs in this phase, though the possibility that there may be some

sulphonation by sulphur trioxide in the organic phase has not been discounted 55.

The isomer distributions obtained in sulphonations of toluene are summarized in table 2.

The xylenes have been purified by sulphonation with 80% acid, which sulphonates the meta-isomers almost

exclusively. Extraction with water followed by desulphonation leads to almost pure mexa-xylene 56,57.

Xylene sulphonic acids may also be obtained by the sulphonation of the corresponding acetyl derivative with 85% acid

and the acetyl group is ejected.

g. Napthalene

Much work has been carried out into the sulphonation of naphthalene because of the importance of the napthalene

sulphonic acid as dyestuffs intermediates. The usual sulphonating agents are oleum or sulpuric acid, and the attack is

usually on the more election rich 1- position. However, at temperatures above 1000c and with time, the 1- acid

rearranges to the thermodynamically more stable 2- acid 62 . The 1- acid does not rearrange at an appreciable rate at

300c63.

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Table 2: Isomer distributions in the sulphonation of toluene

Reagents Temple O P M

H2SO4 : 98.8% 58 25 49.3 5.2 45.5

95.8% 58 5 51.6 4.7 43.7

25 50.2 4.9 44.9

85.5% 58 225 38.8 2.6 58.6

65 30.5 4.4 65.1

92.3% 4 25 32.0 2.9 65.1

77.6% 58 25 2.2 2.1 76.7

65 16.4 4.3 79.3

94.0% 48 200 5.0 54.0 41.0

74% 59 141 3.2 59.6 37.2

SO3 in SO2 3, 53 -80 38.0 2.0 60.0

-10 3.8 0.0 96.2

SO3 in CHCl3 53 20 - - 95

SO3 gas 60 40-55 12.0 9.3 79.3

ClSO3H 61 35 37.5 3.8 58.8

The isomer distribution obtained in the sulphonation of naphthalene with chlorosulphonic acid in dicholoroethone is

given in table 3.

Table 3: Isomer distribution in the sulphonation naphthalene 64.

Temperature (0c) Rxn Time (Hrs) % Total Yield % 2- isomer in Yield

-35 5 74 1.8

-25 4 75 4.4

-20 4 85 6.5

-15 3 88 9.3

-10 1 51 10.9

0 2 73 12.0

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The pure sodium salt of naphthalene sulphonic acid has been prepared by carrying out the sulphonation in chloro

sulphonic acid in dicholoroethane at -300c with a molar ratio of 1.25 acid : 1 napththalene: 0.5 solvent – under this very

mild conditions; no 2- sulphonic acid is made65. Cerfortain and Telder 66 attribute this preference for 1-substitution to the

difference in enthalpy of activation of the two possible isomers. The difference in partial rate factors decreases with

increasing acid concentration. The same study showed that the sulpho group deactivates the ring to which it is attached

more effectively than the adjacent ring. For this reason, disulphonation leads to a sulphonic acid group in each ring 67.

1- naphthylamine can be tri-sulphonated, the ring carrying the amino group also carrying two of the sulphur groups68.

Hydrolysis leads to the removal of just one sulpho group, and gives a mxture of disulphonic acid.

Similarly, the disulphonation of 2-napththol leads 2- napththol -3, 6- disulphonic acid 69.

The presence of a nitro group in the napththalene ring deactivates the ring to which it is attached. Thus, 1- nitro-

napththalene sulphonates to give a mixture of the 1, 5, 1, 6- and 1, 7- nitro napththalene sulphonic acids 70.

The rules for the poly sulphonation naththalene have been stated by Gilbert 2 as (i) the second sulpho group will not go

ortho, para to the existing sulphno group, and (ii) the second sulpho group renters the unslphonated ring.

Sulphone formation occurs with the sulphonation of naphthalenne 71 as would be expected by analogy with benzene.

SULPHONATION OF HETEROCYCLES

a. Pyridine and derivatives

Pyridine and many of its derivatives cannot be sulphonated at tempetatures below 2000c because of the formation of a

sulphur trioxide complex, but at these higher temperatures the complex rearranges to the 3- sulphonic acid. The

reaction is probably intermolecular. Thus, in a typical reaction, pyridine was sulphonated directly by sulphur trioxide

at 225-2350c in the presence of HgSO4 catalyst to give pyridine -3- sulphonic acid 72 .

An improvement on this procedure is to use excess sulphur trioxide using a mercury catalyst, at 170-180%; the

pyridine:: sulphur trioxide complex first formed (I) is sulphonated in the 3- position by the excess sulphur trioxide. The

N-sulpho group is then removed by hydrolysis to give the pyridine -3- sulphonic acid in good yield 73.

N N N N

SO3 SO3

SO3H SO3H

+ SO3

SO3 H2O

+ H2SO4

II

Pyridine – N- oxide, 2- methyl pyridine and quinoline can be similarly sulphonated. Pyridine – N- oxide has also been

sulphonated with 21% oleum, again using a mercury salt as a catalyst. Refluxing for 22 hours at 220c gives the pyridine

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– N – oxide – 3 – sulphonic acid74. Canonical forms such as ( III) indicate that 4- substitution would be expected; the 3-

substitution is explained by prior protonation of the N- oxide, which destroys the resonance with the ring 75.

N N N

O O OH

H

III

It has been shown that at 3300c pyridine -3- sulphonic acid rearranges to give the thermodynamically more stable 4-

acid 76. Drastic conditions are required because the reaction probably involves a desulphonation – resulphossnation

process, and both these processes are hindered by the electron withdrawing inductive effect of the ring nitrogen.

Pyridines which are disubstituted in the 2- and 6- positions with bulky groups cannot form a complex with sulphur

trioxide; thus it is not surprising that 2, 6- di-tertbutyl pyridine is found to sulphonate under very wild conditions

(sulphur trioxide in liquid sulphur dioxide at -100c) to give the 3 – sulphonic acid 77 (22). This is almost the only case of a

sulphonation leading to the introduction of the –SO3H group next to such a large alkyl group. Even the introduction of

a chlorine in the 4- position does not prevent sulphonation in the 3 – position (in about 12% yield) 78. This is surprising

as 4- chloro -2, 6-, lutidine gives only a trace of 3- sulphonic acid after treatment with 21% oleum for 24 hours at 1900c 74.

It might have been expected that 2, 6, ditertbutyl pyridine – 3- sulphur acid would rearrange to the 4- acid under much

milder conditions than required for pyridine – 3- sulphonic acid, because of the steric crowding. However,

sulphopnation of 2, 6 ditert butylpyridine with sulphur trioxide in a sealed tube at 240 – 2500c for 15 hours gives none

of the expected product, but instead a 15-20% yield of compound IV 79.

NMe3CMeMe

O2S

CH2

IV

As would be would be expected, quinoline is sulphonated in the benzene ring than the hetero cyclic ring, as the electron

–withdrawing inductive effect of the nitrogen is increased further by its protonation by the oleum used for the

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sulphonation. Qunoline -5- sulphonic acid is the product except in the presence of certain mercury salts, when the 8-

sulphonic acid is formed. 80 3 – methyl – isoquinoline similarly yields the 5 – acid when treated with 50% oleum 81.

4, 4’ – bipyridyl gives a 20% yield of 4, 4’ – bipyridyl – 3,3’, 5,5’ – tetra sulphonic acid when subjected to a drastic

sulphonation (concentrated suphuric acid at 3000c) 82. Similar conditions on 3,3’ bipyridyl gives an 84% yield of 3,3’

bipyridyl – 5 sulphonic acid 83.

Little work has been done as the sulphonation of pyrimidine, but some of its derivatives have been sulphonated and

chlorosulphonated with chlorosulphonic acid 84. The results are summaried in Table 4.

Table 4: Sulphonation of pyrimidine derivations with ClSO3H

Derivatives Temp (%) Product Yield

2 – NH2-6OH-4-CH3 110 5-sulphonic acid 43-44%

2-NH2-6-OH 110 5-sulphonic acid 34%

2,6 diamino -5-CH3 110 5-sulphonic acid 40-43%

2,6 –diamino-4-CH3 125 5-sulphonic acid 36%

2-NH2-4-CH3 125 5-sulphonic acid -

b. Pyrrole

Pyrole is more acid resistant than furan, and 2-accetyl – pyrrole can be sulphonated in good yield using 6% oleum 85 but

the usual reagent is s

SO3. pyridine, the reaction being carried out in a sealed tube at 1000c over 5-10hours. At lower temperatures with this

complex, pyrrole gives the unstable N-sulphonic acid 86 which rearranges at higher temperatures to give pyrrole –2-

sulphonic acid.

Sulphonation of pyrrole occurs preferentially in the 2- and 5- positions and, as with furan and thiophene, when these

positions are blocked sulphonation proceeds in the 3- and 4- postions with SO3.pyridine 87. This contradicts an earlier

paper by the same workers 86 where 2, 5 dimethyl pyrrole was stated to be inert to SO3. pyridine even at 1500c.

Data on the sulphonation of some pyrode derivation is given in Table 5.

Indole is similarly acid sensitive and is usually sulphonated with SO3.pyridine to give the 2-sulphonic acid. If this

position is blocked, then sulphonation is difficult to achieve; thus 2- methylindole will not sulphonate with

SO3.pyridine at 1100c 88 which is surprising as 2-phenyl indole gives the 3- sulphonic acid in 95% yield with the same

reagent at 120-1300c 89.

The preliminary step in these sulphonations appears to be the formation of the N- sulphur derivative, followed by

rearrangement 88 ..

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Carbazole is quite stable to strong sulphonating reagents, and ca be sulphonated with oleum. Polysulphonation is quire

common, with up to two sulpho groups in each benzene ring. Again the first stage appears to be the formation of a

sulphanate 90.

Borodkin91 has used chlorosulphonic acid to sulphonate and separate a synthetic mixture of carbazole and anthracene,

the carbazole being more easily sulphonated. Data on the sulphonation of indole and carbazole derivatives are given in

Table 6.

c. Furan

Furan and many of its derivatives are sensitive to acid conditions, and direct sulphonation has been possible only with

the intrpduction of sulphur trioxides complexes, particularly the pyridine one.

Table 5: Sulphonation of pyrrole & derivatives.

Derivatives Reagent Temp (0c) Products Yield %

Pyrole 86 Py.SO3 100 2-SO3H 90

Methyl 86 Py.SO3 100 2-SO3H 57

2-Methyl 86 Py.SO3 100 5-SO3H 54

2,4- dimethyl 86 Py.SO3 100 5-SO3H -

2,5-dimethyl 87 Py.SO3 100 3-SO3H 47

- 3.4-(-SO3H)2 11.6

1,2,5-trimethyl 87 Py.SO3 100 3-SO3H 40

- 3.4-(-So3H)2 12

2,3,5-trimethyl 87 Py.SO3 100 4-SO3H 25.4

2.chloro 92 Py.SO3 60-70 5-SO3H 40

2-phenylazo 92 Py.SO3 70-80 5-SO3H 50

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1-phenyl 86 Py.SO3 100 2141-(SO3H)2 25

1-orthotolyl 86 Py.SO3 100 2-SO3H 4.5

1-acetyl 85 Py.SO3 100 2151-(SO3H)2 -

2-acetyl 85 Py.SO3 100 2141-(SO3H)2

3,5,(SO3H)2

-

2-acetyl 85 6% oleum - 4-SO3H 75

Table 6: Sulphonation of indole, carbozole and their drivatives


Indole 88 Py.SO3 120 2-SO3H 90

1-acetyl-indoline93 Cl SO3H 50-60 4-SO3cl 54

2-Phenyl 89 Py.SO3 120-130 3-SO3H 95

3-acetic acid89 Py.SO3 100-110 2-SO3H 55

1-acetyl 89 Py.SO3 130-110 2-SO3H 50

3-methyl 88 Py.SO3 120 2-SO3H 55

Carbazole90,94,95 40% oleum 15 2,3,6,8-

(SO3H)4

90

ClSO3H (1 mole) - 3-SO3H 85-87

ClSO3H (3/4 mole) - 3,6-(SO3H)2 85-98

PhNme2+ClSO3H - 9-SO3H 86

Conc. H2SO4 90 1,3,6-(SO3H)3 -

Thus in one study 96 both furan and coumarone gave only a resinous polymer with sulphuric acid, and tars are the

only product when 2-acetyl furan is treated with sulphuric acid of sulphur trioxide in dichloro-ethane 97.

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A thorough investigation has been made of sulphonating agents for furan98. Sulphuric acid gives only tars, while

DMF – Sulphuric acid and pyridine – sulphuric acid complexes do not react, even at 1200c, while excess acid causes

tar formation. Sulphur trioxide yields tars, with traces of sulphonic acids, even when acetic onlydride is used as a

solvent. SO3.pyridine only sulphopnates furan when the two compounds are exactly in a 1:.1 molar ratio; excess

pyridine or traces of sulphur trioxide hinder the reaction.SO3.trimethylamine gives only 15% of furan sulponic acid

after treatment at 1000c for 2 hours, whilst SO3 dioxan is too reactive and only gives tars wth traces of sulphonic

acids. Picoline.SO3 acts as the pyridine complex.

2- furoic acid is remarkable in that it may be sulphonated with sulphur trioxide or chloro sulphonic acid to give 5-

sulpho – 2-furoic acid 99. This indicates that the aromatic ring is very deactivated towards elecetro phillic attack,

perhaps due to such species as A.

O

O

O

H

A

Furfural, however, shows the usual sensitivity to strong sulphonating agents, and can only be sulphonated in poor

yields by SO3. Pyridine which must be pure 97. Traces of sulphuric acid inhibit the reaction, showing that it is not

simply an electron-withdrawing effect of the carbonyl group that is responsible for the stability of 2-furoic acid.

In general, furan derivatives have to be sulphonated using SO3. pyridine. The complex and the furan deriviative

are heated together in a sealed tube at 1000c, usually for about 10 hours100-102. These sulphonations are summarized

in Table 7.

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Table 7:.


Furan 98 Me3N.SO3 100 2-SO3H 15

Furan 100 Py.SO3 100 2-SO3H 30-90

2-methyl 102 Py.SO3 in ClCH2CHCl 30-40 5-SO3H -

2-methyl 102 Py.SO3 100 5-(SO3H)2 -

2,5-dimethyl 102 Py.SO3 100 3-SO3H -

2-carboxylic acid97 SO3 in clcH2cH2cl 140 5-SO3H 82.5

Furfural 96 Py.SO3 - 5-SO3H 20

Furfuraldiethylacetate

or diacetate 103

Py.SO3 - Mono or di

sulphonic

acids

-

Coumarone 101 Py.SO3 100 2-SO3H -

Dibenzofuran 104 H2SO4 100 2-SO3H 75

d. Thiophene

Thiophene is very much more stable to acid conditions than either pyrrole or furan, and has consequently been studied

far more than those heterocycles. However, sulphuric acid still cannot be used as a resinous polymer in formed 96

thiophenes have been sulphonated using fluoro-sulphonic acid, chlorosulphonic acid, sulphur trioxide and various

complexes of the latter, in good yields. With chlorosulphonic acid the stable sulphonyl chloride is usually formed.

Thiophene 2-carboxylic acid readily acid-hydolyes to thiopene 102.

Displacement of a substituent in the sulphononation reaction is not common, but a tert-butyl group is displaced in the

sulphonation of 3-tertbutyl thiophene with sulphur trioxide in dichloroethane 105. 2,5-ditert butyl thiophene

sulphonotes in the 3-position in 75% yield with sulphur trioxide in dichnoethane. The 5-position is sterically very

crowded. Rather surprisingly, this reaction also occurs with SO3.pyridine, a relatively mild sulphonating agent.

The sulphonations of thiopene and its derivatives are summarized in table 8.

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Table 8:.


Thiophen 106 ClSO3 0 2-SO3Cl 37

Thiophen 108 SO3 20 2-SO3Cl 50

Thiophen 108 Py.2SO3 20 2-SO3H 86

Thiophen 109 *D.SO3 20 2-SO3H 75

2-Cl 111 **Py.SO3 120 5-Cl-2-SO3H 94.8

2-Br111 Py.SO3 100 5-Br-2-SO3H 90

2-I 111 Py.SO3 100 5-I-2-SO3H

+Disproportionation

77

2,5-dichloro 113 Py.SO3 10 3- SO3H 66

2-Nitro 115 CISO3H/CHCl3 Reflux 2,4-(SO2Cl)2 74

2-acetamido 115 ClSO3H 80-90 3,5-(SO2Cl)2 31

2,5- dimethyl109 Py.SO3 130 3- SO3H 75

2,5- dimethyl109 Py.2SO3 - 3- SO3H 94

2,5- dimethyl109 D.SO3 - 3- SO3H 95

2,5-di t-butyl105 48%SO3 in

ClCH2CH2Cl

- 3- SO3H 75

*D.SO3 = Dioxan.SO3

**Py.SO3 = Pyridine.SO3

Desulphonation

The desulphonation reaction is not well understood .Industrially, the reaction is widely used, the sulphonic acid group

being removed by boiling with water under pressure, and with acid catalysis. The process involves desulphonation-

resulphonation. Thus, high temperatures and having something to solvate the sulphur dioxide (thereby reducing its

activity) leads to desulphonation predominating..

An early study by Baddeley, Holt and Kenner 117 on the desulphonation of meta-cresol sulphonic acid concentration,

proportional to the hydrogen ion activity of the solution, and independent of the nature of the inorganic anion. They

proposed the following mechanism equation.(1)

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ArSO3 + H3O Ar Ar-H + H2OSO3O

SO3

H

H

H

equation (1)

Spryskov and Ovsyuankina118 agree with Baddeley proposing that protodesulphonation proceeds via the ion sulphonic

acid and H3O+.

A more recent study 119 on the desulphonation of benzene sulphonic acid and the toluene sulphonic acid also agrees

with the findings of Baddeley et al, but proposed that the dependence of desulphonation rate upon acid concentration

was more compatible with the protronating species being H3SO+4 instead of H3+O as above.

Both sets of workers agree that the reaction must go via a Wheland-type intermediate such as found in equation (1).

Partial rate factors had been determined for the protodesulphonation of the toluene sulphonic acid and tert butyl-

benzenesulphoric acid 119. These, indicate that for a particular ethyl group, fo> fp>> fm.

Spryskov and kachurin 120attempted to find a medium in the rate of protodesulphonation of orthochloro benzene

sulphoric acid using S35 labelled sulphoric acid, but disulphonation interfered with the study, and thus, a well defined

rate was not found.

Sulphone formation

The formation of sulphones (compounds of the general formula ArSO2Ar) from the sulphonation of aromatic

hydrocarbons with vigorous reagents in the most troublesome side reaction encountered industrially. Simple diaryl

sulphones are often valueless industrially, and so their formation, and separation from the sulphoric acid, represents a

substantial economic loss. If diaryl sulphones are required, they may be manufactured in very good yield by refluxing

an aromatic sulphonyl chloride with our aromatic hydrocarbon in the presence of a Friedel-Crafts catalyst such as ferric

chloride121,122 . Aluminum trichloride121,123, Titanium tetrachloride122, Bismuth trichloride 124 or Antimony pentachloride

124. This method permits the formation of mixed diaryl sulphones.

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Mechanism

In a study on the sulphonation of benzene with sulphur trioxide, Cerfontain and his co-workers16 showed that the ratio

of diphenyl sulphone to benzene sulphonic acid increased with an increase in the initial sulphur trioxide : benzene

ratio. This led to the proposed mechanism in equation (2) with a pyrosulphonate as an intermediate:

SO3ArH + Ar

H

SO3Ar

H

SO3SO3

ArSO3SO3H

ArSO3H SO3 ArSO2Ar + H2SO4

ArH

+

SO3[I]

equation (2)

This is in agreement with an earlier paper15 which suggests a similar pyrosulphonate mechanism. The evidence for such

a pyrosulphonic acid intermediate such on( I) in equation (2) is very convincing; for example;: Jolly et al 17 prepared

highly reactive compounds of the type ArSO3 SO3Na (Ar = 4- chlorophenyl or paratolyl) by a peculiar insertion

reaction of sulphur trioxide into the ArSO3 Me molecule.

ArSO3Me + SO3 ArSO3SO3Me

These pyrosulphonate esters, which cannot lose sulphur trioxide as easily as free pyrosulphonic acid, react readily with

aromatic compounds to give sulphones is over 80% yield.

This insertion reaction has also been used to prepare methyl chloropyrosulphonate by the reaction of methyl chloride

with two moles of sulphur trioxide125. This reacts with aromatic compounds to yield sulphones of the general formula

Ar (SO2Me)n, where n-=1 to 4.

Jolly et al17 suggested that the pyrosulphonic aid cleaves to give a sulphonium ion, which then leads to the sulphone in

equation (3)

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+ HSO4ArSO3SO3H ArSO2

ArH

Sulphone

………….. equation (3)

In this case, one might expect sulphone formation to be first order with respect to pyrosulphonic acid, and hence with

the aryl sulphonic acid. However, a careful kinetic study has not yet been undertaken. An investigation on a semi-batch

scale126 indicated that the reaction is indeed first order with respect to the sulphonic acid. Further support for a

sulphonium ion mechanism comes from a study of the reactions of ArSO2OCOCF3127 a mixed anhydride made by

reacting an arylsulphonic acid with trifluoroacetic acid. The anhydride reacts with aromatic hydrocarbons to give

sulphones, probably by the prior loss of CF3COO- but one can not rule out the possibility of a bimolecular reaction in

which the extremely electron-deficient sulphur atom acts as an electrophyllic centre, and the last step is the loss

CF3COO-.

Just as there is more than one mechanism leading to aromatic sulphonation with sulphur trioxide, so sulphone

formation is similarly complicated. Thus Christen Sen128 has provided tracer evidence for a pyrosulphonic acid

intermediate in sulphone formation in the sulphonation of iodobenzene with sulphur trioxide, but also puts forward

evidence indicating that the sulphonic anhydride also present leads to sulphone formation. The proposed mechanism is

given in equations (4) and (5)

2 RSO3H + SO3 (RSO2)2O + H2SO4.......(4)

R

O

R

SO2

SO2

SO3

R

O

R

S

SO2

O

OS

O

OO

RSO2 + RSO3SO3H+

………………..(5)

Reaction in equation (4) also probably proceeds via a short lived pyrosulphonate intermediate.

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This proposal that sulphone formation may go via the sulphonic acid anhydride is supported by the fact that benzene

sulphonic anhydride, benzene and aluminum trichlorodride when refluxed together gave diphenyl sulphone in good

yield129

Methods of reducing sulphone formation

Tukenaka 126 has calculated the apparent activation energy for the sulphonation of benzene with sulphuric acid in the

temperature range 170-2100c to be 14.8 Kcals mole-1, and that of sulphone formation to be 16.2 kcals mole-1 under the

same conditions. Thus it may be expected that high temperatures would favour sulphone formation and that low

temperatures would favour sulphonation. Diphenyl sulphone has in fact been made industrially by sulphonating

benzene with 95% acid using benzene vapour in a column at 2600c 130.

The direction of the addition is also very important in general; the addition of the hydrocarbon to sulphur trioxide gives

half as much sulphone as the verse procedure 131. This is explained by applying the law of mass action to equation (5).

Industrially, the most important method of reducing sulphone formation is the addition of ionic sulphates or

bisulphates to the reaction mixture. These have the effect of reversing the decomposition of the pyrosulphonic acid by a

common ion effect as given in equation (6).

ArSO3SO3H ArSO2 + HSO4 .....................(6)

The addition of 0.05 mole % of solid anhydrous sodium sulphate per mole of benzene, for example: reduced sulphate

formation from 24% to 3.5% when sulphur trioxide was used as the sulphonating agent132. It is clear that the anion

rather than the camion is inhibiting sulphone formation, as in the sulphonic acid-sulphonation or benzene. Sodium

bisulphate, potassium sulphate and lithium sulphate all had a marked effect but sodium benzene sulphonate had ion

effect on the amount of benzene formed 126. The effect of addition of sodium sulphate is clearly seen in Table 9133.

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Table 9

No of moles of

Na2SO4 per mole

Of C6H6

Temperature (0c)

Time (Hrs)

% sulphone*

0 90 3 24.2

0.001 90 3 21.3

0.05 90 3 15.1

0.10 90 1 9.8

0.10 120 2 9.8

0.25 90 1 5.5

0.25 120 2 5.5

0.50 90 3 1.7

0.50 160 3 17

*The sulphone is diphenyl sulphone -3,3’ disulphonic acid.All the above results are for 2.5 moles So3 per mole of C6H6.

In sulphonations, many sulphur trioxide, much smaller amounts of sodium sulphate are needed to reduce sulphone

formation than for 65% oleum-sulphonations 132. Thus it may be that sulphone formation occurs mainly in the organic

phase and it is the sulphate ion concentration in this phase which is important in reducing sulphone formation. In the

case of oleum sulphonations, the sulphate ion would be ,mainly in the acid phase.

Rueggeberg and his co-workers131 have shown that organic aids considerably decrease sulphone formation. They

accounted for this in equatuion (7)

ArSO3SO3H + RCOOH ArSO3H + RCOOSO3H

H2SO4 + RCOAr ArSO3H + RCOOH

(a)

ArH ArH(b) (c)

equation (7)

Steps 7(a) and (c) are thought to be more important..It is known that sulphur trioxide reacts with acetic acid at below 00c

to form acetyl sulphate compounds analog to RCOOSO3H in equation (7)134 and that the readily sulphonates aromatic

hydrocarbons with little sulphone formation.

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No systematic study to correlate sulphone formation with the strengths of sulphur trioxide complexes has been carried

out. The more reactive of these complexes, for example, those with DMF or bis – (2-chloroethyl) ether may prove to be

useful in keeping sulphone formation down because of their easily regulated reactivity.

Heterocyclic compounds do not yield sulphones as by-products of sulphonations. This may be because only mild

reagents can be used to sulphonate them. So the sulphur trioxide concentration is never high enough to allow

pyrosulphonate formation; this is because all the sulphur trioxide in the system is rapidly removed by the formation of

a hetero atom: sulphur trioxide complex.

Chloro sulphonation

The chloro sulphonations of aromatic compounds is of great industrial importance, for instance, sulphonyl chlorides

are used in the preparation of sulphonates and sulphones; many of which have medicinal uses.

The usual reagent used to introduce the – SO2Cl group is chlorosulphonic acid which has the advantage of being cheap.

Mechanism

Equimolar quantities of chlorosulphonic acid and the aromatic compound yield the sulphonic acid in good yield,

especially at low temperatures. It is likely, therefore, that in the preparation of aromatic sulphonyl chlorides by using at

least two moles of chlorosulphonic per mole of aromatic compound,the sulphonic acid is formed as an intermediate.

Harding135 proposed the following mechanism for the reaction with toluene in equations (8) and (9)

C6H5CH3 + HSO3Cl CH3C6H4SO3H + H2SO4 ...............(8)

CH3C6H4SO3H + HSO3Cl CH3C6H4SO2Cl + H2SO4...............(9)

Equation (8) might be expected to go to completion as the HCl should be evolved. However, it is quite common for a

solvent to be used to facilitate easy stirring and HCl is soluble in many organic solvents. Equation (9) is an equilibrium

which may be disturbed. Lukashevich 8 proposed a mechanism which involve a pyrosulphonate intermediate, as in the

sulphonatiopn of aromatic compounds with sulphur trioxide. He proposed the reaction scheme found in equations

10 – 13.

ArH + ArSO3H + HCl ................(10)ClSO3H

ArSO3H + ClSO3H ArSO3SO3H + HCl ...............(11)

ArSO3SO3H + ClSO3HArSO2Cl + H2SO4 .................(12)

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ArSO3SO3H + ArH ArSO2Ar + H2SO4...............(13)

It was found that the addition of sulphonic acid or hydrochloric acid reduced the yield sulphonyl chloride and

sulphones, which was explained by suggesting the pyrosulphonate intermediate, ArSO3SO3H, was decomposed by

strong acid, thereby hindering reaction in equations (12) and (13). Harding135 would have explained this by saying the

acid added reverses equilibrium.

Lukashevich also found that sulphonic acid anhydrides were formed in the reaction of chlorosulphonic acid and with

halogenated aromatic hydrocarbon; this may provide a second mechanism whereby sulphonates are formed in these

chlorosulphonation reactions . The work of Christen Sen refers128 Sulphonic acid anhydrides tend to be stable in

strongly acid media and this would explain why one gets less sulphone formation when acids are added.

Methods of increasing yields sulphonyl chlorides

The reaction in equation (9), being an equilibrium reaction has attracted much interest in the possibility of distutrbing

the equilibrium to achieve higher yields of sulphonyl,halides. This would be more economical than increasing the

chlorosulphonic acid concentration. Two methods have been used to remove sulphoric acid produced. In one of these136

, carbon tetrachloride is added to the reaction mixture; this is oxidised by sulphuric acid to give phosgene in equation

(14)

RH + ClSO3H + CCl4 RSO2Cl + COCl2 + 2 HCl ..............(14)

This method has the obvious disadvantage that phosgene is highly toxic. The second method is to add sodium chloride

or sodium sulphate 7. The sodium chloride reacts with the sulphoric acid to give sodium sulphate and HCl, and the

sodium sulphate gives sodium bisulphate. Using 0.1 mole sodium chloride as an additive, 2.6 moles of 92%

chlorosulphoric acid on 1 mole of toluene gave a total yield of 87% ortho-and para-toluene sulphonyl chlorides137.

However, the reaction took a total of 24 hours, far longer than is economial industrially.

de Jong 138 has increased the yield of sulphonyl chloride by extracting it with a haloalkane or cycloalkane as it is

formed. Thus by agitatig orthotoluene sulphoric acid with chlorosulphonic acid in carbon tetrachloride for 1 hour at

400c, and separating the organic and aqueous layers and further extracvting the aqueous phase; and finally distilling the

carbom tetrachloride off under reduced pressure, an 89% yield of ortho toluee sulphonyl chloride waso btained.

Using 2.5 moles of chlorosulphonic acid per mole of sodium para toluene sulphonate, the maximum yield of sulphonyl

chloride was only 80% 139 and it may be worthwhile industrially to consider other methods of chlorinating sulphonic

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acids. For instance, DMF catalyses chlorination with thionyl chloride ,and generally this method gives excellent yields

of sulphonyl chlorides in one or two hours. In a patent140 describing the use of DMF, sulphur trioxide to sulphonate

toluene, a yield of 70% para toluenesulphyonyl coloride was obtained and the total yield of sulphonyl chlorides was

not stated.

Conclusion

There are well over a thousand importance publications on this work this century, with the result that this

survey has had to be very selective and concentrated on those papers of theoretical or great industrial

importance. For this reason indirect methods of introducing the sulphonic acid group such on the oxidation of

sulphides or the use of diazoniun salts have not been considered.

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84. Khromov, N.V, and Karlinskaya, R.S., Zhur. Obshch. Khim., 24 2212, (1954) reported in Chem. Abstr., 50, 355 (1956)

85. Terent’ev, A.P and Yanovskaya, Zhur. Oshch. Khim., 19, 2118 (1949), reported on Chem. Abstr., 44, 3973, (1950).

86. Ibid, 19 538 (1949) reported in Chem. Abstrf., 43, 7015, (1949)

87. Ibid, 19 1365 (1949), reported in Chem. Abstr., 44, 1095 (1950)

88. Ibid, 19, 781 (1949), reported in Chem. Abstr., 44, 1095 (1950)

89. Ibid, 21, 1295 (1951), reported in Chem. Abstr., 46, 2048 (1952)

90. Borodkin, V.F., J. Applied Chem USSR, 23, 803, (1950) reported in Chem. Bstr., 46, 8089 (1952)

91. Ibid, 23, 807 (1950)

92. Terent’ev, A.P and Yanovaskaya, I.A., Zhur. Oshch. Khim. 21, 281 (1951) reported in Chem. Abstr., 45, 7025 (1951)

93. Terent’ev, A.P and Preobrazhenskaya, M.N, Zhur. Oshch. Khim., 30, 1218 (1960), reported in Chem. Abstr., 55, 511

(`1961)

94. Karpukhin, P.P and Levochenko, O.I, Kghim. Piom. Namu. Tekhol. Zb., 18 (1963), treported in BCem Abs5tr., 59,

7461 (1963)

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95. Borodkin, V.F, and Mal’kova, T.L, Zhur. Priklad. Khim. 21, 849 (1948), reported in Chem. Abstr., 43, 6205 (1949)

96. Jurusek, A, and Kovak, J , Sb. Prac. Chem. Fak. SVST, 41, (1961)0 rerported oin Chem. Abstr., 58, 2420 (1963)

97. Terent’ev, A.P, Kazitsyna, L.A. and Turouskaya, A, Vestrik Moskou. Uniu., 3, 159 (1948) reported in Chem. Abstr,

44 5862, (1950).

98. Terent’ev, A.P, Kazitsyna, L.A. and Suvorova, S.E. Zhur. Obshch. Khim., 19, 1951 (1949), see in Chem. Abstr., 44,

1954, (1950)

99. V.S.P. 2,623,050 (1952)

100. Terent’ev, A.P, Kazitsyna, L.A. and Suvorova, S.E. Zhur. Obshch. Khim., 18, 723 (1948) reported in Chem. Abstr., 43

215 (1949).

101. Ibid, 19, 531, (1949)s reported in Chem. Abstr., 43, 7015 (1949)

102. Kazitsyna, L.A, Vestnik. Moscov.UMV., 109 (1947) repoted in Chem. Abstr., 42, 3751 (1948).

103. Jurasek, A., Kovac, J, Kada, R., and Frim, R., Chem Zvesti. 18 214 (1964) repoeted in Chem. Abstr., 61, 3054 (1964)

104. Wenland, R.T and Smith, C.H., Proc. North Dakota Acad. Sci., 2, 40 (1949) reported in Chem. Abstr., 43, 5021, (1949)

105. Gol’dfarb, Y.L., Antik, L.V and Konstatinov, P.A., Izvest. Akad. Nauk. SSSR Otdel. Khim Nauk, 624 (1956),

reported in Chem. Abstr., 51 1138 (1957)

106. Blatt, A.H, Bach, s and Kresch, L.W., J. Org. Chem., 22, 1694 (1957)

107. Ger.P. 1,088, 509, (1958)

108. Terent’ev, A.P, and Kadatskii, Zhur. Obshch. Khim., 22,153 (1952) reported in Chem. Abstr., 46, 11178 (1952).

109. Ibid, 23, 251 (1953), reported in Chem. Abstr, 146, 11178 (1952).

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110. U.S.P. 23,480,465 (1949).

111. Terent’ev, A.P, and Kadatskii, G.M., Zhur. Obshch. Khim., 12, 21, 1524 (1951) reported in Chem. Abstr., 46, 2536

(1952).

112. Ger. P. 1,088,508 (1958).

113. Truce, W.E, Lotspeich, F.J., J. Amer. Chem. Soc., 77, 3410 (1955)

114. Buzas, A, and Teste, J, Bull. Soc. Chim. France, 793 (w1960)

115. Lew, H.Y. and Nolter, C.R., J. Amer. Chem. Soc., 72, 5715 (1950)

116. Sone, C, and Natsuki, Y, Nippon Kagaku Za schi, 83, 496, 1962 reorted in Chem. Abstr, 59, 3862 (1963)

117. Badddley, G, Holt, G, and Kenner, J., Natyure, 154, 361 (1944)

118. Spryskov, A.A., and Ovysyankina, Sb. Statei Obshch. Khim., 2, 882 (1953), reported in Chem. Abstr., 49, 6894 (1955)

119. Wanders, A.C.M and Cerfontain, H, Rec. Trav. Chim., 86, 1199 (1967)

120. Spryskov, A.A, and Kachurin, O.I, J. Gen. Chem. VSSR, 28 1693 (1958)

121. Austr. P. 242,187 (1962)

122. U.S.P. 3,125,604 (1964)

123. Sen, A.B, and Roy, A.K, J. Ind. Chem. Soc., 33, 687 (1956)

124. B.P. 979,111 (1965)

125. Addition to Fr. P. 1,211,412, Addition 75,120 (1961)

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126. Takenaka, J., Kogyo Kugaku Zasshj, 70 483 (1967) reported in Chem. Abstr., 67, 7682 (1967)

127. Bourne, E.J., Stacey, M., Fatlow, J.C./, and Tedder, J.M., J. Chem. Soc., 718 (1951)

128. Christen Sen, N.H., Acta Chim. Scand.,18, 954 (1964)

129. Field, L., J. Amer. Chem. Soc., 75, 394 (1952)

130. U.S.P. 2,593, 001

131. Rueggeberg, W.H.C., sauls, T.W., and Norwood, S.L., J. or g Chem., 20 455 (1955)

132. B.P. 679,826 (1952)

133. Shestov, A.P and Osipova, N.A., J. Gen. Chem. USSR, 29 591 (1959)

134. Van Poshi, A.J., Rec. Trav. Chem., 40,103 (1921)

135. Hatrding, L., J. Chem. Soc., 1261 (1961)

136. Ger. P. 757, 505 (1952)

137. Kissin, B., and Pomeratsev, Khim, Nauka ; Prom, 2,809, (1957) reported in Chem. Abstr., 52, 11770 (1958)

138. de Jong, Belg. P. 634,880 (1963)

139. Shivjiana, B.H and Shah, R.C., J. In. Chem. Soc., Ind. and News Ed., 17, 127 (1954)

140. B.P. 1,073,003 (1967).

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