Dehydration of Secondary Alcohols

8/13/2019 Dehydration of Secondary Alcohols

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ON THE MECHANISM OF DEHYDRATION OF SECONDARYALCOHOLS OVER ALUMINA CATALYST 11.

EFFECT OF STRUCTURE ON R TE

K . KOCHLOEFL, M. KRAUS, CHOU CHIN-SHEN**, L. BERANEK and V. BAZANTInstituteo Chemical Process Fundamentals Czechoslovak Academy o Science Prague

Received February 21st, 1961The effect of the structure of 14 secondary alcohols on the rate of their

dehydration on y-alumina has been determined. The compounds studiedincluded some aliphatic alcohols, cyclic alcohols of various ring size andsome stereoisomeric alkylcyclohexanols. Activation energies have beenestimated and the reactivity of the alcohols has been compared on the basis ofreaction rate constants for 200. The effects of vicinal carbon atom substitution, of ring size and of steric configuration of the reacting molecule arediscussed. The results indicate that the geometry of the reacting moleculeis of major importance in the dehydration of alcohols on solid catalysts.

qn of the most fruitful approaches to the elucidation of reaction mechanisms inorganic chemistry has been the study of structure effects on reactivity. This approachis extensively used for homogeneous transformations and it was to be expected thatits application to heterogeneous catalytic reactions would equally contribute to a better understanding of such processes.

For catalytic dehydration of alcohols some very divergent mechanisms have beenproposed recently see1- 3 none of which explains satisfactorily all experimentalfacts. Further work is therefore necessary and in this paper kinetic measurementsof the dehydration of a series of secondary alcohols are described. By varying thestructure of the reacting compound, the influence of carbon chain branching, ofring size and of configuration was studied.

Kinetics of primary and secondary alcohol dehydration over alumina has previously beenstudied by Bork and Tolstopjatova4 ; these authors have found the same activation energy valuesfor all primary alcohols and another for aU secondary alcohols. However, from the small numberof substances reported in their paper no conclusions concerning the effect of the structure ofcarbon skeleton on the reaction rate can be derived. Recently, Miller 5 and Laible6 have studieddehydration of some alcohols on silica-alumina catalyst. Unfortunately, their results form nobasis for consideration of structure effects on reactivity.

Part L: This Journal 25, 2513 1960).On leave of absence from the Institute of Applied Chemistry, Chang-ehun, China.

Vol. 27 1962) 1199


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Kochloe/l, Kraus, Chou Chin-Shen, Beranek, Balant:xperimental

Boiling points and melting points values are uncorrected.The purity of all substances used was controlled by gas-liquidchromatography.Prepara t ion of Cyclic Alcohols

Cyclopentanol was prepared by sodium reduction of cyclopentanone in aqueous methanolether solutions. Yield 75 , b. p. 139-1400 /760mm.

Cyclohexanol. A commercial product was converted into cyclohexyl acetate which was fractionated on a column of 30 TP. The fraction boiling 1735/760 mm was hydrolysed with sodiumhydroxide solution and the alcohol destilled through the same column. B p. 160 -1605 m. p.20, nfio 14650.

Cycloheptanol and cyclooctanol were prepared by reduction of the corresponding ketones withlithium aluminium hydride9 in 94 and 954 yield, respectively: Cyc1oheptanol boiled at88 0/18 mm, cyc1ooctanol at 1 3 -104/15 mm.

For the preparation of cyc1oheptanone and cyc1ooctanone the standard ring enlargement ofcyc1ohexanone by means of diazomethane was used10 11. The composition of the reaction products as determined by gas-liquid chromatography for different cyc1ohexanone-diazomethaneratios is shown in Table 1 The crude reaction mixture was fractionated on a destillation columnof 30 TP and the individual ketones were purified as semicarbazones. Cyc1oheptanone, b. p.63 -64 12mm; semicarbazone,m.p. 1635 (methanol). Cyc1ooctanone, b.p.100 -1005 35 mmm. p. 34; semicarbazone, m. p. 1710 (methanol).

2,2-Dimethylcyclohexanol. 2-Methylcyc1ohexanone was methylated12 yielding 65 of 2,2-dimethylcyc1ohexanone, b. p. 1695/740 mm, which was reduced by lithium aluminium hydrideto the alcohol in 90 yield. B p. 169 -172/750 mm.

Preparation of Aliphatic Alcohols2-Methylhexanol- 3). An attempt to purify the product of the reaction of isopropylmagnesium

bromide with butyraldehyde13 (yield 46 ) by distillation was unsuccessful. t was thereforeconverted to the corresponding ketone by potassium bichromate oxidation in dilute sulphuricacid14 . The 2-methylhexanone-(3) obtained was then purified as the semicarbazone by crystallisation from methanol; m. p. 117 -118. Reduktion of the ketone by lithium aluminium hydrideafforded 2-methylhexanol-(3) in 92 yield; b. p. 144/760 mm.

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Table IComposition of the Crude Reaction Product from the Reaction of Cyc1ohexanone

with DiazomethaneMolar ratio of diazomethane to cyc1ohexanone: A 116, B 232.

Compound A B

Cyc1ohexanone 05 0Methylenecyc10hexane epoxide 51 06Cyc1oheptanone 788 50Methylenecyc10heptane epoxide 39 76Cyc100ctan one 89 820Cyc1ononanone 28 48

,Collection Czechoslov. Chern. Commun.


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Mechanism o Dehydration o Secondary Alcohols over Alumina Catalyst. 11Heptanol- 4). The crude product obtained by the reaction of propylmagnesium bromide with

ethyl formate15 was purified using the same method as above. Heptanone-(4), b. p. 144/760 mm;semicarbazone, m. p. 132 (methanol). Heptanol-(4), b. p. 153 -153 5/748 mm.

2,4-Dimethylpentanol- 3) was prepared from isopropylmagnesium bromide and isobutyraldehyde 16 . Fractionation on a column of 20 TP afforded the pure alcohol, b. p. 1384 -138 8/744 mm, in 68 yield.

Preparat ion of Stereoisomeric Alkylcyc1ohexanolsFor kinetic measurements 40 - 80 g of the pure alcohols were required and the known methods

for the preparation of the stereoisomeric alkylcyclohexanols were therefore modified to makethem more suitable for large scale work. In general, a crude mixture enriched in one of the stereoisomers was transformed into the crystalline ester which was then purified by repeated crystallisation.

Table IISodium Reduction of the Ketones in Absolute Ethanol

Ketone Alcohol Yield Alcohol Composition,trans cis

2 Methy cyclohexanone 780 880 1204 Methylcyclohexanone 823 871 1294-t-Butylcyclohexanone 742 927 7'3

Table IIIHydrogenation of the Ketones on Platinum Black in Acetic Acid-Hydrochloric Acid Mixture

Ketone Alcohol Yield Alcohol Composition,cis trans

2 Methy cyclohexanone 863 950 504-t-Butylcyclohexanone 812 94'5 4'52-t-Butylcyclohexanone 943 810 190

The crude products for the preparation of trans-comp ounds were obtained by reduction of thecorresponding alkylcyclohexanones with sodium in absolute ethanol17 (see Table II). For thepreparation of cis-compounds the ketones were hydrogen ated on platinum black in acidic medium(see Table III). In the case of trans-2-methylcyclohexanol the difference in esterification ratesof the stereoisomers was made use of for its isolation fro m the product of o-cresol hydrogenation.

The starting alkylphenols were hydrogenated on a Raney-nickel catalyst in ethanol at 80and 150 atm. The unreacted alkylphenol and the corresponding ketone formed as by-productwere separated from the alcohol by the usual procedure. The isomer composition of the alcoholsis given in Table IV.Vol. 27 (1962) 1201


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Kochloe/l, Kraus, Chou Chin-Shen, Berdnek, Bazant:Table IV

Hydrogenation of Alkylphenols on Raney-nickel

Alkylphenol Alcohol Composition,cis trans

o-Cresol 250 750p-Cresol 320 680p-t-Butylphenol 295 705o-t-Butylphenol 300 700

trans-2-Methylcyclohexanoltrans-2-Methylcyclohexanol p-nitrobenzoate. To a mixture of dry pyridine (145 ml) and 2-

methylcyclohexanol (114 g, 1 mole, 75 trans-isomer a solution of p-nitrobenzoyl chloride(120 g, 0649 mole) n dry benzene (500 ml) was added dropwise under cooling and mixing.Mter standing for 20 minutes, the reaction product was poured on a mixture of hydrochloric acid(180 ml) and ice. The benzene layer was separated, washed with sodium hydrogen carbonatesolution and the unreacted alcohol and benzene were removed by steam distillation. The p-nitrobenzoate was :filtered off; yield 137 g (521 ). Analysis of a hydrolysed sample indicated a contentof 93 of trans-isomer in the ester. Four crystallisations from methanol afforded pure trans-2-methylcyclohexyl p-nitrobenzoate (80 g), m. p. 635 - - 64.

trans-2-Methylcyclohexanol. The p-nitrobenzoate (256 g, 0973 mole) was refluxed \\,'itha solution of potassium hydroxide (112 g, 2 mole) in water (900 ml) and methanol (400 ml). Aftertwo hours, the methanol was distilled off through a column; the remaining mixture was dilutedwith water and the trans-2-methylcyclohexanol taken up in ether. The pure product was obtainedby destillation in 55 yield (615 g); b. p. 165/750 mm, r; 5 = 372 cPo

cis-2-Methylcyclohexanol.2-Methylcyclohexanone was prepared by potassium bichromate oxidation of crude 2-methyl

cyclohexanol in dilute sulphuric acid14 in 812 yield. The ketone was purified as the semicarbazone, m. p. 1915 (methanol). The yield of the pure 2-methylcyclohexanone was 664 , b. p.160 -161 /746 mm.

Hydrogenation of 2-methylcyclohexanone. The ketone (130 g, 116 mole) was hydrogenated onplatinum black catalyst (14 g) at atmospheric pressure and room temperature in glacial aceticacid (600 ml) to which 80 ml of pure hydrochloric acid was added. When the hydrogen uptake hasceased the catalyst was :filtered off and the solution diluted with water (600 ml). The oily layerwas separated, the aqueous layer was neutralised with sodium hydroxide solution and extractedwith ether. The combined products were washed and dried. Ether was distilled off and the residuewhich contained some 2-methylcyclohexyl acetate was hydrolysed with potassium hydroxidein a water- methanol solution. Working up of the crude product yielded 114 g (853 ) of 2-methyl- .cyclohexanol (95 cis-isomer .

cis-2-Methylcyclohexyl 3,5-dinitrobenzoate. To a mixture of the above alcohol (1472 g, 129mole and pyridine (300 ml) a solution of 3,5-dinitrobenzoyl chloride (300 g, 13 mole) in benzene(1000 ml) was a::lded under cooling. After standing for 3 hours, the reaction product was workedup in the same manner as in the case of trans-2-methylcyclohexyl p-nitrobenzoate. Five-fold recrystallisation from methanol yielded 267 g (672 ) of the pure cis-ester, m. p. 975 - 980.

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Mechanism of Dehydration of Secondary Alcohols over Alumina Catalyst. II.cis-2-MethylcyclohexatlOl. The 3,5-dinitrobenzoate (267 g, 0868 mole), potassium hydroxide

(112 g, 2 mole), water (900 ml) and methanol (3400 ml) were refluxed for two hours. The yieldof the pure alcohol was 743 g (75 ), b. p. 162/740 mm, r; 5 = 172 cPo '

trans-4-Me thylcyclohexanol4-Methylcyclohexanone was prepared from the crude alcohol in the same way as 2-methyl

cyc1ohexanone; yield 730 . An alternative preparation by oxidation with chromium trioxidein acetic acid afforded only 442 of the ketone.

trans-4-Methylcyclohexyl hydrogen phthalate was obtained from 4-methylcyc1ohexanol (composition see Table II) and phtalic anhydride in pyridine by the standard method The crudeproduct was purified by four-fold crystallisation from a light petroleum-ethyl acetate mixture5: 1). Yield 436 m. p. 1105 -1195.

trans-4-Methylcyclohexanol was prepared from the above ester by hydrolysis with alkaliin 841 yield. B. p. 172-173/760 mm.

trans-4-t-Butylcyclohexanol4-t-Butylcyclohexanone was obtained from crude 4-t-butylcyc1ohexanol by chromium trioxide

oxidation in acetic acid21 in 80 yield and purified as the semicarbazone, m. p. 212 (methanol).The pure ketone has b. p. 92/ 10 mm, m. p. 495.

trans-4-t-Butylcyclohexyl hydrogen phthalate was prepared from the alcohol (see Table II)by the standard method. Five-fold crystallisation from light petroleum-ethyl acetate 5 : 1) afforded560 of the pure trans-isomer, m. p. 146.

trans-4-t-ButylcyclohexanoI2 . The ester was hydrolysed with alkali and the alcohol isolatedby the same method as trans-2-methylcyc1ohexanol. Yield 950 , m. p. 815 -820 (light petroleum).

cis-4-t-ButylcyclohexanolThe crude alcohol (Table III) was converted to the hydrogen phtalate, purified and hydrolysed

in the same way as the trans-isomer. Hydrogen phtalate, m. p. 141 -142; cis-4-t-butylcyc10-hexanol, overall yield 838 , m. p. 81 - 82.

cis-2-t-Butylcyc lohexanol2-t-Butylcyclohexanone was obtained from the alcohol by oxidation with chromium trioxide

in acetic acid17 . The crude product (yield 803 ) was converted to the semicarbazone, m. p.181 -182 (methanol). Hydrolysis of the semicarbazone gave the pure ketone in 640 yield;b. p. 105 -106/38 mm.

cis-2-t-Butylcyclohexyl p-nitrobenzoate. The same method as for cis-2-methylcyc1ohexanol3,5-dinitrobenzoate was used. Yield 384 , m. p. 885 - 890 (ethanol).

cis-2-t-Buty cyc ohexanoI 7. Alkali hydrolysis of the p-nitrobenzoate afforded the pure alcoholin 897 yield; m. p. 560 - 570 (light petroleum).

CatalystThe same lot of a ~ o m m e r c i l y-alumina catalyst as in our previous work7 was used.

Analytical MethodsThe course of the preparation of all compounds and of their purification was control1ed after

each step or operation by gas chromatographic analysis of the products. Glycerol was used as.the stationary phase, celite as the support, and nitrogen as the carrier gas (see22); the temperatureVol. 27 (1962) 1203


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Kochloe/l, Kraus, Chou Chin-Shen, Beranek, Bazant:of the column and the gas velocity was waried according to the boiling point of the particularalcohol or ketone.

Conversion in kinetic measurements was calculated from determinations of the unreactedalcohol by the acetylation method23 For the aliphatic and simple cyclic alcohols 25 27 foldmolar excess of acetic anhydride and one hours reaction time gave satisfactory results. For thesubstituted cyclohexanols the acetylation time had to be 15 hour. In the case of cis-2-t-butylcyclohexanol a 13 fold molar excess of acetic anhydride and 5 hours of reaction time were necessary for complete reaction.

ProcedureThe apparatus used for kinetic measurement is described in our previous paper7 The partial

pressure of the reacting alcohol was adjusted by addition of a suitable amount of toluene. Asa sample for analysis the middle fraction of the reaction products corresponding to steady stateconditions) was separated and pyridine added until the aqueous and toluene layers disappeared.With this homogenised sample two or three parallel determinations were performed.

At different temperatures kinetic measurement included usually 4 different parcial pressuresfor which two to four separate conversiondeterminations were made. An example ofexperimental values for trans-2-methylcyclohexanol is presented in Fig. 1 The pointsrepresent averages from two to four conver-

Q 6 . - - - - - - - - . - - - - - - - - - - - - - - - - - ~x

sion measurements. 0 4

Fig. 1 QDehydration of trans-2-MethylcyclohexanolConversion x) dependence on reciprocal

space velocity W/F). 1 193C, 2 204C,32145C. 0 3

Kinetic Equationt was ascertained by preliminary experiments that a linear relationship exists between reci

procal space velocity contact time) and conversion of the reacting alcohol approximately toa value of the latter quantity of 04. At constant temperature a single line in conversion againstreciprocal space velocity graphs was obtained for different parcial pressures of the alcohol in thefeed. t was therefore possible to calculate the rate constant k by means of the integral equation

k = xF/W 1)where x is the conversion of the alcohol, F the feed rate of the alcohol [mole/h] and W the volumeof the catalyst bed [1]

On the basis of Langmuir-Hinshelwood kinetics of catalytic reactions an equation of thistype can be obtained in two cases: 1. For a irreversible reaction if the rate determining step isdesorption of the products from the surface of the catalyst. In this case, the x-W/F plot shouldbe linear in the whole range of conversions; however, this condition is not fulfilled here. 2. Fora irreversible reaction if a the rate determining step is a surface reaction, b the alcohol is adsorbedon a single center, c the adsorption coefficient of the alcohol is high in general and higher than

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Mechanism of Dehydration of Secondary Alcohols over Alumina Catalyst. II.the adsorption coefficient of water, and d) the olefin formed is practically not adsorbed. In suchcase it is possible to Omit the terms 1 KRPR and KsPs in the basic rate equation

(2)where KA, KR and Ks denote adsorption coefficients of the alcohol, water and the olefin, respectively, and PA PR and Ps the corresponding partial pressures. Equation (2) simplifies to

r k (3)which on integration gives Equation (1).

For higher water contents, i. e. for higher conversions, it is not possible to omit the term KRPR;this gives

4a)After rearrangement we get

4b)For confirmation ofthis hypothesis the experimental data of 4-methylcyclohexanol dehydration

from our previous paper were used. The reaction conditions in these experiments were: temperature 215C, partial pressure of the alcohol P = 0095 atm, dilution with toluene and nitrogen.In the x W F plot the tangent was found for wiF = 0 which practically coincided with a curvedrawn through experimental points up to x = 03. This gave with the help of equation (1) thevalue of the k. Additional tangents were measured at points of x = 04 and 0 6, respectively,and from their values and equation 4b) an estimate of KRIKA ratio was obtained (approximately0 5). Using this value and the rate constant, the dependence of the x on the wl was calculatedand good agreement with all experimental points was obtained.

From this we conclude that dehydration of secondary alcohols over our y-alumina catalyst isgoverned by a surface reaction as the rate-determining step. This confirms that our kinetic datadescribed the rate of a chemical reaction and not the rate of adsorption or of any other process.

Results nd iscussionA comparison of the appropriate values for the aliphatic alcohols (Table V and

Fig. 2) shows no substantial influence of chain branching in the neighbourhood of thehydroxyl group on the rate and activation energy. This indicates that electroniceffects, which usually play an importantrole in liquid phase reactions, have littleinfluence under our conditions.

Fig. 2Arrhenius Plots of Rate Constants for Ali-

phatic and Simple Cyclic Alcohols1 Heptanol-(4), 2 2-methylhexanol-(3), 32,4-dimethylpentanol-(3), 4 cyclopentanol, 5 cyclohexanol, 6 cycloheptanol, 7 cyclooctanol,

8 2,2-dimethylcyclohexa?ol.

Vol. 27 (1962)

-1 0 . . . - - . - - - -- - . - - - - - - - . - - - - - - - .- - - - -logk

0 5

o

-0 5

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Kochloejl Kraus Chou Chin-Shen Beranek Baiant:Table V

Rate Constants and Activation Energies of Secondary Alcohol Dehydration over y-Aluminak k re1Alcohol for 200 0

mole/h Ifor 200 0 kcal /mole

Heptanol- 4) 049 10 332-Methylhexanol- 3) 051 10 342,4-Dimethylpentanol- 3) 065 13 32Cyclopentanol 095 19 36Cyclohexanol 051 10 35Cycloheptanol 119 23 35Cyclooctanol 437 86 -2,2-Dimethylcyclohexanol 047 09 34trans-2-Methylcyclohexanol 092 18 44trans-4- Methylcyclohexanol 096 19 38trans-4- t-Buty1cyclohexanol 105 2 38cis-2-Methylcyclohexanol 617 121 2cis-2-t-Buty1cyclohexanol 202 403 9cis-4-t-ButyIcyclohexanol 692 136 27

A more marked dependence may be observed on the ring size of simple secondarycyclic alcohols. However, the values of activation energy are practically the samefor all members of this group and differ only slightly from those for the aliphaticalcohols. The order of reactivity for the cyclic alcohols is in agreement with observations of ring size influence on some related reactions in solution reported by variousauthors25 - 28. Quantitative treatment of our findings is not yet possible, not even forthe liqujd phase reactions a satisfactory explanation has been presented althoughsome hypotheses have been proposed25 26.

From the similarity between the activation energy values for both aliphatic andsimple cyclic alcohols we assume that the mechanism of the dehydration of this twogroups of substances is identical or, if more mechanisms are in operation, the degreesof their participation are of the same magnitude.

In studying the dehydration of 2,2-dimethylcyclohexanol we intended to determinewhether a decrease in the number of hydrogen atoms in the neighbourhood of thehydroxyl group will influence the reaction rate. From comparison of the values i t;lTable V for cyclohexanol and its 2,2-dimethyl derivative is evident that the presenceof a quaternary carbon atom diminishes the reactivity only slightly.

t appeared further important to study the dehydration of those alcohols whichhave a fixed position of the hydroxyl group in respect to other atoms in the molecule.This condition is not fulfilled in the case of the aliphatic alcohols where there is no


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Mechanism o Dehydration o Secondary Alcohols over Alumina Catalyst. II.powerfull restriction to an arbitrary arrangement of the molecule on the surface of thecatalyst; Even in the case of unsubstituted cyclic alcohols the position of the hydroxylgroup is not strictly defined because of ready interconversion of different conformations 9 The same is true for 2,2-dimethylcyclohexanol.

For these reasons we studied the dehydration of some stereoisomeric 2- and 4-alkylcyclohexanols (Table V and Fig. 3 . The t-butylcyclohexanols were most suitablebecause of their conformational homogeneity: the cis-isomers have the hydroxylgroup in the axial and the t-butyl group in the equatorial positions whereas bothsubstituents of-the trans isomers are equatorial. Since the bulky t-butyl group couldexert specific effect on the reaction rate we also examined the dehydration of the corresponding 2- and 4-methyl derivates. With these compounds steric conditions arenot so clear-cut; however, deviationsfrom conformational homogeneity aresmall enough not to be taken in accountin the present study.

Fig. 3Arrhenius Plots of Rate Constants for Ste-

reoisomeric Alky cyc1ohexanols1 trans-2-Methyicyc1ohexanol, 2 cis-2-methylcyc1ohexanol, 3 trans 4 t butylcyc1ohe-xanol, , 4 cis-4-t-butylcyc1ohexanol, 5 cis2-t-butylcyc1ohexanol, 6 trans 4 methy1cyc1o

hexanol, 7 cyc1ohexanol.

1 0lo k

2

a

0 5

2 05

Largest differences in reaction rates and activation energies were found amongstereoisomeric alkylcyclohexanols. Table V shows that on the average the activationenergy of the cis-isomers is substantially lower than that of the trans isomers. For thealiphatic and simple cyclic alcohols this quantity has values between those for thealkylcyclohexanol stereoisomers. Such distinct dissimilarity in activation energiesof individual conformations is clearly connected with a different geometry of reactingmolecules and we regard it as evidence for different mechanisms of dehydration.One can suppose that for the formation of the activated complex on the surface ofthe catalyst a specific steric arrangement of a reacting molecule is necessary. A lowactivation energy can then be expected in the case of substances in which a suitablegeometry is largely preformed in their free state. However, a precise picture of theform of the activated complex is hardly possible to propose on the basis of the present data since chemisorbed species and not free molecules are involved in its formation; however, this does not mean than the form of the molecule is totally changedby chemisorption.Vol. 27 (1962) 1207


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Koc;hloe/l Kraus Chou Chin-Shen Beranek Bazant:In the series of trans-alkylcyclohexanols our results shows no effect of alkyl struc

ture on the rate whereas the opposite has been observed for the cis-compounds.To explain this fact we assume a different behaviour of the hydrogen atoms vicinalto the OH group which mayor may not take part in the formation of the activatedcomplex. The first possibiljty probably holds for the cis-alcohols while no participation of these hydrogen atoms has to be expected for the trans-isomers. Then for thissecond group of alcohols some type of non-synchronous mechanism must be valid;for example, it may involve the formation of a surface alkoxide like that proposedby Topcijeva3o 3 1 or the formation of a bridged carbonium ion17 However, on thebasis of our previous results 7 we exclude the possibility of a classical carboniumion mechanism which has been proposed by Brey and Krieger 32 to explain dehydration over solid catalysts.

In the case of the dehydration of cis-alkylcyclohexanols a synchronous mechanismis probable, for example of the type that has been proposed by Eucken33 or quiterecently by Pines 3

High reaction rate of the cis-2-t-butylcyclohexanol dehydration cannot be explainedsolely by suitable geometry of the molecule but steric effects of the bulky alkyl grouphave evidently also to be considered. In this Laboratory a similar phenomenon wasobserved in the case of the catalytic dealkyla60n of 2-t-butylphenoI34 .

Unfortunately, a comparison of our results with corresponding measurements ofdehydration in the liquid phase is not possible as no equivalent study has been published until now, although a number of papers has been devoted to the mechanismof the homogeneous dehydration of alcohols2 ,17 ,3s -38 . Growing evidence from ourand other authors kinetic studies indicates (see34 , 3 9 - 42 that specific structure effectshaving no direct analogy to reactions in solution may playa decisive role in heterogeneous catalytic reactions.

We wish to thank Dr J Sicher Institute o Organic Chemistry and Biochemistry Prague orhelpful discussions in the course o our work and in interpretation o results.We are further indebted to Dr R. Komers or gas-chromatographic analysis and to Miss V Mikoto va or technical assistance.

References1. Winfield M. E.: Catalysis Vol. VII (P. H. Emmet ed.) p. 93. Reinhold, New York 1960.2 Naro P. A., Dixon J. A.: J. Am. Chern. Soc. 81, 1681 (1959).3 Pines H.: J. Am. Chern. Soc. 82, 2401 (1960).4 Bork A. Tolstopjatova A. A.: Acta Physicochim. URSS 8, 603 (1938).5 Miller D. N .: Thesis. University of Wisconsin 1955.6 Laible J. R.: ThesiS. University of Wisconsin 1958.7. Beranek L., Kraus M. Kochloefl K. Bazant V.: This Journal 25, 2513 (1960).8 Nenitcescu c. Ionescu C. N.: Bull. soc. chim. Romania 14, 65 (1932).9. Smith P. Bauer D. R.: J. Am. Chem. Soc. 74, 6135 (1952).

10. De Boer J . Th ., Backer J. H .: Org. Syntheses 34, 24 (1954).11. Kohler E. P., Tishler M., Potter H. Thomson H . T.: J. Am. Chern. Soc. 61, 1057 (1939).12. Bailey W., Medoff M.: J. Am. Chern. Soc. 76, 2708 (1954).


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Dehydration of Secondary Alcohols

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