Acetylation method

The replacement of active hydrogen of compounds belonging to the class ROH (phenols or alcohols), in addition to compounds of the category RNHg and RgNH (i.e., primary- and secondary-axranes may be acetylat directly, whereby the reactive H-atom is specifically 

In true sense, the acetylation of alcohols and phenols is really regarded as a specific instance of esterification by virtue of the fact that the resulting acetyl derivative 

R2N—C — CHg, respectively, that may be regarded as mono- and di-substituted derivatives 

In actual practice, acetylation may be accomplished by two major procedures, namely Procedure-I. Heating with a mixture of Acetic anhydride and Acetic acid  

It has been observed that when a primary or secondary amine is reacted with glacial acetic acid by the application of heat, the corresponding acetyl derivative is obtained however, the ensuring reaction is invariably found to be extremely sluggish and slow, as given below  

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Uses. The lowest member of this class, ketene itself, is a powerful acetylating agent, reacting with compounds containing a labile hydrogen atom to give acetyl derivatives. This reaction is used only when the standard acetylation methods with acetic anhydride or acetyl chloride [75-36-5] do not work weU. Most of the ketene produced worldwide is used in the production of acetic anhydride. Acetic anhydride is prepared from the reaction of ketene and acetic acid. 

A. Gr. Perkin s Acetyl method. (Arur. Chem. Sot-., 1904, 20, 171). The method consists in hydiolysing the acetyl derivative in presence of alcohol and di.stilling off the ethyl acetate and then estimating the quantity by hydrolysis. 

Finally, prochiral bis(hydroxymethyl)phenylphosphine oxide 82 was desym-metrisized using either a lipase-catalysed acetylation (Method A) or hydrolysis of the corresponding diacetyl derivative 83 (Method B), to give the chiral monoacetate 84. Application of the two reverse procedures made it possible to obtain both enantiomerically enriched forms of 84 (Equation 40). ... 

After prolonged degassing of a large batch of PPG, analyses showed that its hydroxyl, unsaturation, and water contents were 0.97 meq/g, 0.033 meq/g, and 0.0035%, respectively. The hydroxyl content was determined by an acetylation method, carried out with acetic anhydride (10). The amounts of unsaturation and water were determined by the mecuric acetate and Karl Fischer methods (10), respectively. The obtained analytical results indicate that the number-average molecular weight of the dihydroxy material is 2062, provided its molecular weight is arbitrarily assumed to be twice that of the monohydroxy material, and that the mole fraction of the monohydroxy poly (propylene oxide) is 0.066. This value corresponds to a number-average functionality of 1.93 for the PPG. 

Hydroxyl groups were determined by the acetylation method described by Blom et al. (I). The procedure consisted of treating 1-gram samples with acetic anhydride-pyridine reagent. The acetylated sample was recovered by filtration and thoroughly washed. The amount of hydroxyl function was then determined by hydrolyzing the sample with 0.2N sodium hydroxide and measuring the amount of acetic acid liberated when the hydrolyzate was neutralized with sulfuric acid and steam distilled. 

Dr. Fester The acetylation method used would include phenolic hydroxyl. However, the total hydroxyl for kerogen was less than 5% of the total oxygen and less than 2% for trona acids. If present, phenolic hydroxyl would represent only a small part of the total oxygen. 

Hydroxyl Group Determination. The procedure described below is a modification of the acetylation method of Verley and Bolsing 35) and of the amended version of Freudenberg and Schliiter 18). 

Figure 3.6 Examples of water solubilizing structures and the routes used to introduce them into the lead structures. O-alkylation, N-alkylation, O-acylation and N-acylation reactions are used to introduce both acidic and basic groups. Acetylation methods use both the appropriate acid chloride and anhydride.

Sulfuric acid is a powerful esterification catalyst. It has been widely applied with mixtures of acetic acid and acetic anhydride to promote acetylations of numerous substances. Use of this catalyzed reaction for starch acetylation, however, has not risen to pre-eminence among starch acetylation methods as it has done among cellulose acetylations, although both reactions were discovered at the same time. The underdevelopment of this reaction in the starch field may be due to the following causes (1) sulfuric acid, a powerful acetylation catalyst, strongly catalyzes the hydrolysis of starch molecules and cannot be used for starch acetylations in the concentrations found most effective for cellulose reactions (2) most investigations of this reaction have been made on whole granules... 

Barnett acetylation method. Acetylation of hydroxy compounds such as cellulose with acid anhydrides in the presence of chlorine and sulfur dioxide. With cellulose, the process yields the diacetate below 65C and the triacetate above this temperature. 

The following sections shall exclusively deal with the elaborated syntheses of certain medicinal compounds prepared by using the acetylation methods, such as Acetanilide, Acetylsalicylic acid (Aspirin) Acetylacetone Phenacetin, Acetylcysteine and Paracetamol. 

As already discussed in Section 8.2.2, the number of peaks in a chromatogram increases considerably on derivatization. Figure 8-12 shows the chromatogram of a sample before and after acetylation. Method B (Table 8-6) will give increased separation using a slowly rising temperature-pressure program. 

This sample preparation method (Method 1) is the result of several experiments. An attempt was also made to extract the deproteinated sample with alkali (Method 2) without previously extracting with toluene. As a comparison, an experiment was carried out in which the toluene phase was evaporated to dryness and then acetylated (Method 3). The results are given in Table 9-5. The criterion was again the recovery rate. 

Testillano. P. S., Gonzalez-Melendi, P Ahmadian, P., and Risueano. M. C. (1995). The methylation-acetylation method An ultrastructural cytochemistry for nucleic acids compatible with immunogold studies./. Struct. Biol. 114(2), 123-139. 

Another CTA preparation is the fibrous acetylation method. In this process part or all of the acetic acid is replaced with an inert diluent, e.g., toluene, benzene or hexane to maintain the cellulose fibrous structure during the reaction. Perchloric acid is usually employed as the catalyst in this process. This process is used exclusively for the preparation of cellulose triacetate. 

Acetylation methods have been used for many years to improve some properties of wood cellulose such as moisture repellency, dimensional stability and resistance to environmental degradation. Their use for improving the properties of natural fibers has increased significantly in the last decade or so. The methods are based on the reaction of lignocellulosic material with acetic anhydride at elevated temperature, with or without a catalyst. The acetic anhydride reacts with the more reactive hydroxyl groups according to the equation [36],... 

Another method of establishing structures depends upon the well-defined reaction of benzenediazonium chloride with acyclic phenylhydrazones to form diphenylformazans (215) no well-defined product is obtained from cyclic isomers. This method has given the same results as the acetylation method, and, in addition, has shown that the third isomer of glucose phenylhydrazone is also cyclic. 

GPC has not so far been successfully applied directly to the phenolic polymers because of their highly polar and strongly hydrogen bonding character. Condensed tannins will dissolve only in very polar solvents (Sect. 1,123) and the best defined GPC supports are based on polystyrene or polystyrene bonded to silica. However, several groups have derivatized condensed tannins by methylation (66) or peracetylation (36, 124, 142, 148) and performed GPC analyses on the relatively less polar derivatives in chloroform or tetrahydrofuran. The usual acetylation method is with pyridine and acetic anhydride. 

Table 3.1 compares hydroxyl values obtained by three methods. In every case the acid-catalysed acetylation method gives a higher result than that obtained by phthalation, the mean difference between the two methods being 2.5% of the determined value. Agreement between the p-toluene sulfonic acid method and the phenyl isocyanate method is good. 

Molecular weight p-Toluene sulfonic acid-catalysed acetylation method. Average hydroxyl value (mg KOH/g) Phthalation method. Average hydroxyl value (mg KOH/g) Reaction with phenyl isocyanate. Average hydroxyl value (mg KOH/g)... 

Table 3.4 Comparison of the V8HQ method with the acetylation method ...

We have studied, in detail, the formation of poly(propylene ether) dlols by the reaction of propylene oxide with 1,5-penta-nedlol catalyzed by the hexacyanometalate complex Zng[Co(CN)3Ig 2.1 (CH30C CHg0CH3)0.85 ZnCla. 0. The hydroxyl type present in the dlols, prepared with this catalyst, has been found by Siggla s acetylation method (2) to be almost exclusively secondary, with only i -10 of the hydroxyls being of the primary type. 

Molecular weight p-Toluene sulfonic acid catalysed acetylation method Phthalation method [2] Reaction with phenyl isocyanate... 

Table 1.13 - Comparison of the V8HQ Method with the Acetylation Method...

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