This article was downloaded by: [Pennsylvania State University] On: 24 May 2013, At: 01:01 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Phosphorus, Sulfur, and Silicon and the Related Elements Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gpss20 Poly-(N,N′-dibromo-N-ethyl- benzene-1,3-disulfonamide) and N,N,N′,N′- Tetrabromobenzene-1,3- disulfonamide as Highly Efficient Catalysts, and (AC 2 O/SIO 2 ) as a Heterogeneous System for the Acetylation of Alcohols, Amines, and Thiols Under Microwave Irradiation Hojat Veisi a , Ramin Ghorbani-Vaghei b , Hosna Eskandari b , Saba Hemmati a , Ardashir Rezaei b , Somaye Hajinazari a , Mohammad Raoof Heidari Far a & Azam Entezari a a Department of Chemistry, Payame Noor University (PNU), Iran b Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran Published online: 19 Feb 2011. To cite this article: Hojat Veisi , Ramin Ghorbani-Vaghei , Hosna Eskandari , Saba Hemmati , Ardashir Rezaei , Somaye Hajinazari , Mohammad Raoof Heidari Far & Azam Entezari (2011): Poly-(N,N′- dibromo-N-ethyl-benzene-1,3-disulfonamide) and N,N,N′,N′- Tetrabromobenzene-1,3-disulfonamide as Highly Efficient Catalysts, and (AC 2 O/SIO 2 ) as a Heterogeneous System for the Acetylation of Alcohols, Amines, and Thiols Under Microwave Irradiation, Phosphorus, Sulfur, and Silicon and the Related Elements, 186:2, 213-219 To link to this article: http://dx.doi.org/10.1080/10426507.2010.496277 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden.
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This article was downloaded by: [Pennsylvania State University]On: 24 May 2013, At: 01:01Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and theRelated ElementsPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/gpss20
Poly-(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) andN,N,N′,N′- Tetrabromobenzene-1,3-disulfonamide as Highly EfficientCatalysts, and (AC2O/SIO2) as aHeterogeneous System for theAcetylation of Alcohols, Amines, andThiols Under Microwave IrradiationHojat Veisi a , Ramin Ghorbani-Vaghei b , Hosna Eskandari b , SabaHemmati a , Ardashir Rezaei b , Somaye Hajinazari a , MohammadRaoof Heidari Far a & Azam Entezari aa Department of Chemistry, Payame Noor University (PNU), Iranb Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali SinaUniversity, Hamedan, IranPublished online: 19 Feb 2011.
To cite this article: Hojat Veisi , Ramin Ghorbani-Vaghei , Hosna Eskandari , Saba Hemmati , ArdashirRezaei , Somaye Hajinazari , Mohammad Raoof Heidari Far & Azam Entezari (2011): Poly-(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) and N,N,N′,N′- Tetrabromobenzene-1,3-disulfonamideas Highly Efficient Catalysts, and (AC2O/SIO2) as a Heterogeneous System for the Acetylation ofAlcohols, Amines, and Thiols Under Microwave Irradiation, Phosphorus, Sulfur, and Silicon and theRelated Elements, 186:2, 213-219
To link to this article: http://dx.doi.org/10.1080/10426507.2010.496277
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.
POLY-(N,N ′-DIBROMO-N-ETHYL-BENZENE-1,3-DISULFONAMIDE) AND N,N,N ′,N ′-TETRABROMOBENZENE-1,3-DISULFONAMIDE ASHIGHLY EFFICIENT CATALYSTS, AND (AC2O/SIO2) AS AHETEROGENEOUS SYSTEM FOR THE ACETYLATION OFALCOHOLS, AMINES, AND THIOLS UNDER MICROWAVEIRRADIATION
Saba Hemmati,1 Ardashir Rezaei,2 Somaye Hajinazari,1
Mohammad Raoof Heidari Far,1 and Azam Entezari11Department of Chemistry, Payame Noor University (PNU), Iran2Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University,Hamedan, Iran
GRAPHICAL ABSTRACT
RR'XH
X: O, S, NH
RR'XAc
R: H, alkyl or arylR': alkyl or aryl
method A: TBBDA, Ac 2O, rt, CH3CN
method B: PBBS, Ac2O, rt, CH3CN
method C: Microwave, Ac 2O/ SiO2
SOO
SOO
NNCH2CH2
Br Br
PBBS
)n
)
TBBDA
NS
OOS
OO
N BrBr
Br Br
Abstract Poly-(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) (PBBS) and N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide (TBBDA) are good activators and catalytic reagents forthe acetylation of alcohols, amines, and thiols. The presented method has the advantages ofmild conditions, chemoselectivity, and good to high yields, and uses noncorrosive, inexpensive,recyclable, and environmentally friendly catalysts. We have also demonstrated that combiningSiO2 with microwave energy provides an efficient, fast, convenient, and easy workup procedurefor the synthesis of mono- and disubstituted acetates, acetamides, and thioacetamides.
Protection of alcohols, amines, and thiols using acid anhydrides is of great in-terest to synthetic chemists, and has been applied extensively by organic chemists forover a century.1 For this purpose, catalysts are used for rapid and efficient acylations.Although 4-(dimethylamino)pyridine (DMAP), 4-pyrrolidinopyridine (PYY),2 and pyri-dine3 are the most commonly used catalysts for acylations, other catalysts such asAl(OTf)3,4 La(NO3)3.6H2O,5 3-nitrobenzeneboronic acid,6 I2,7 Cu(BF4)2·xH2O,8 ZrCl4,9
HClO4/SiO2,17 Zeolite,18 Montmorillonite K-10 and KSF,19 and InI320 have been used for
the acetylation of alcohols, amines, and thiols. However, many of these methods requireprolonged reaction times and give rise to metal waste products. Thus, a milder, selective,nonhazardous, and inexpensive method is still in demand.
RESULTS AND DISCUSSION
In this article, we report a convenient method for the O,N,S-acetylation of al-cohols, amines, and thiols with acetic anhydride using poly-(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) (PBBS) and N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide(TBBDA)21–26 as recyclable catalytic reagents at room temperature. In addition, we suc-ceeded in the rapid, high yield preparation of acetates, acetamides, and thioacetamidesusing Ac2O/SiO2 under solvent-free conditions by microwave irradiation (Scheme 1).
RR'XH
X: O, S, NH
RR'XAc
R: H, alkyl or arylR': alkyl or aryl
method A: TBBDA, Ac 2O, rt, CH3CN
method B: PBBS, Ac2O, rt, CH3CN
method C: Microwave, Ac 2O/ SiO2
SOO
SOO
NNCH2CH2
Br Br
PBBS
)n
)
TBBDA
NSOO
SOO
N BrBr
Br Br
Scheme 1
To explore the generality and scope of this reaction, a wide range of structurallyvaried alcohols, amines, and thiols were subjected to acetylation by these procedures. Theresults are reported in Table 1. In this manner, we have succeeded in developing convenientand efficient procedures for the preparation of acetamides (Table 1, entries 1–10). Table 1shows that the yields are good to excellent. It was found that secondary amines (Table 1,entries 5–8) undergo smooth acetylation and give the desired acetamides. No selectivitybetween primary and secondary amino groups during the reactions was observed (Table I,entry 9).
In a similar manner, various substituted aromatic and aliphatic hydroxy compoundsand thiols were acetylated very smoothly under mild reaction conditions and gave thedesired O,S-acetylated alcohols, phenols, and thiols with high yields. The procedures areuniformly effective for the acetylation of primary saturated alcohols (Table 1, entries 25
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ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS 215
Table 1 Acetylation of alcohols, amines, and thiols using TBBDA (method A), PBBS (method B), and aheterogeneous (Ac2O/SiO2) system under microwave irradiation (method C)
Method A Method B Method CTime (min)/ Time (min)/ Time (min)/
Table 1 Acetylation of alcohols, amines, and thiols using TBBDA (method A), PBBS (method B), and aheterogeneous (Ac2O/SiO2) system under microwave irradiation (method C) (Continued)
Method A Method B Method CTime (min)/ Time (min)/ Time (min)/
and 29), an allylic alcohol (Table 1, entry 24), benzylic alcohols (Table 1, entries 18–21),secondary alcohols (Table 1, entries 26–28), phenols (Table 1, entries 22 and 23), and thiols(Table 1, entries 11–17). During this reaction, we did not observe chemoselectivity forcompounds with two different functional groups such as NH, SH, and OH (Table 1, entries11 and 12).
Several attempts to acetylate a tertiary alcohol (Table 1, entry 30) using PBBS andTBBDA in the presence of a solvent (acetonitrile) failed. As shown in Table 1, adamantan-1-ol was however acetylated with excellent yield by using Ac2O/SiO2 under microwaveirradiation.
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ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS 217
Since these reagents contain bromine atoms, which are attached to nitrogen atoms,it is very likely that they release Br+ in situ, which can act as a Lewis acid in the reactionmedium. We expected that this would be sufficient to catalyze the acetylation of alcohols,amines, and thiols.21–26
We observed that PBBS and TBBDA were recyclable catalysts for the acetylation,and the catalytic activities of the reagents after several runs were almost the same as thoseof fresh catalysts.
This methods is mild and compatible with various functional groups such as chloro(Table 1, entries 20 and 21), bromo (Table 1, entry 19), and methoxy (Table 1, entry 2)groups present in the substrate. In general, the acetylations are reasonably fast and clean.No side products were isolated in any reaction.
The method was found to be highly selective for primary alcohols with TBBDA andPBBS as catalysts at room temperature. In a mixture of benzyl alcohol and phenol, theprimary alcohol was completely converted to the corresponding product (Table 2, entry 1).Similarly, benzyl alcohol was acetylated in the presence of cyclohexanol, adamantan-1-ol,and benzylthiol at room temperature (Table 2, entries 2–4).
The advantages of our methods as compared with common methods for the acetylationof benzyl alcohol, benzylthiol, and adamantan-1-ol are shown in Table 3.
Table 2 Competitive acetylation reactions of alcohols with TBBDA (method A) and PBBS (method B)
Entry Mixture Product Time (h) Conversion (%)a
1 1b or 4c 100
0
2 1b or 4c 100
0
3 1b or 4c 90
10
4 1b or 4c 100
0
aThe conversion was detected by TLC and NMR spectroscopy.bThe conversion was complied with TBBDA.cThe conversion was complied with PBBS.
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218 H. VEISI ET AL.
Table 3 Reaction times and yields for previously published methods
Substrate Conditions Reaction time Yield (%) Ref.
Benzyl alcohol InI3/reflux 14 h 82 20Benzyl alcohol NBS/CH2Cl2/rt 4 h 94 13Benzyl alcohol K-10 or KSF/rt 1 h 90 19Benzylthiol AlPW12O40/rt 3 min 89 101-Adamantanol NBS/CH2Cl2/rt 37 h 90 131-Adamantanol AlPW12O40/rt 100 min 92 101-Adamantanol Sc(OTf)3/reflux 18 h 81 27
CONCLUSIONS
In conclusion, we have demonstrated that PBBS and TBBDA are good activators(catalytic reagents) for the acetylation of alcohols, amines, and thiols. The present methodexhibits the additional advantages of mild conditions, chemoselectivity, and good to highyields, and it uses noncorrosive, inexpensive, recyclable, and environmentally friendlycatalysts. We have also demonstrated that combining SiO2 with microwave energy providesan efficient, fast, convenient, and easy workup procedure for the synthesis of mono- anddisubstituted acetates, acetamides, and thioacetamides. Moreover, this protocol introducesa practical and viable green technology of solvent-free reactions.
EXPERIMENTAL
General Procedure for the Acetylation of Alcohols, Amines, and Thiols
by Using PBBS and TBBDA (Methods A and B)
To a solution of the amine, thiol, or alcohol (1 mmol) and acetic anhydride (1 mmol) inCH3CN (2 mL) at room temperature, the activator (PBBA, 0.1 g or TBBDA, 0.1 mmol, 0.05g) was added. The mixture was stirred at this temperature for the period of time specified inTable 1. The reaction was monitored by TLC (hexane/acetone, 4:1). After completion of thereaction, the solvent was evaporated. Then CH2Cl2 (10 mL) was added, and the reagentswere removed by filtration. Evaporation of the solvent under reduced pressure gave theproducts. Further purification was achieved by TLC (hexane/acetone, 7:3).
Preparation of the Ac2O/SiO2 Reagent
Acetic anhydride (1 mL) was added to 1 g of silica gel (mesh 70–230) with stirringfor 1 min at room temperature.
General Experimental Procedure for the Acetylation of Alcohols,
Amines, and Thiols with Ac2O/SiO2 Under Microwave Irradiation (Method C)
The amine, thiol, or alcohol (1 mmol) and the above compounds were mixed thor-oughly and then subjected to the 100% power radiation of a domestic microwave oven (LGCo. microwave, 230 v ∼ 50 Hz, RF output 900 W) for a certain period of time (Table 1).The progress of each reaction was monitored by TLC. After completion of the reaction, theobtained mixture was allowed to cool, was diluted with ethanol, and filtered to remove the
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ACETYLATION OF ALCOHOLS, AMINES, AND THIOLS 219
silica gel. Evaporation of the solvent under reduced pressure gave the pure product withexcellent yield (96–100%).
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