Acetyl groups hydrolysis

Note that p-acetamidobenzenesulphonyl chloride will similarly react with primary and secondary amines, and the products, after hydrolysis of the acetyl group, may furnish notable drugs e.g., the condensation products with 2-amino-pyridine and 2-aminothiazole, after remo al of the acetyl groups, provide the drugs commonly known as sulphapyridine (M B 693) and sulphathidzole respectively. 

Cellulose triacetate is obtained by the esterification of cellulose (qv) with acetic anhydride (see Cellulose esters). Commercial triacetate is not quite the precise chemical entity depicted as (1) because acetylation does not quite reach the maximum 3.0 acetyl groups per glucose unit. Secondary cellulose acetate is obtained by hydrolysis of the triacetate to an average degree of substitution (DS) of 2.4 acetyl groups per glucose unit. There is no satisfactory commercial means to acetylate direcdy to the 2.4 acetyl level and obtain a secondary acetate that has the desired solubiUty needed for fiber preparation. 

Conversion of aniline to acetanilide [103-84-4] by reaction with acetic anhydride, is a convenient method for protecting the amino group. The acetyl group can later be removed by acid or base hydrolysis. 

Sulfaguanidine is prepared by condensation of Ai-acetylsulfanilyl chloride with guanidine ia presence of alkali. The A/ -acetyl group is removed by acid or alkaline hydrolysis. 

Surface Tension. The surface tension of aqueous solutions of PVA varies with concentration (Fig. 10), temperature, degree of hydrolysis, and acetate distribution on the PVA backbone. Random distribution of acetyl groups in the polymer results in solutions having higher surface tension compared to those of polymers in which blocks of acetyl groups are present (74—77). Surface tension decreases slightly as the molecular weight is reduced (Fig. 11). 

Hydrolysis. The primary functions of hydrolysis are to remove some of the acetyl groups from the cellulose triester and to reduce or remove the combined acid sulfate ester to improve the thermal stabiUty of the acetate. 

As mentioned in Section 22.1 the probability of acetylation of any one cellulosic group is strongly dependent on its position in the fibre. Since they cannot be dissolved before acetylation it will be realised that some molecules will be completely acetylated whilst others may be untouched. It is thus necessary first to acetylate completely the cellulose and the resultant triacetate material, which is soluble in certain solvents, may then be back-hydrolysed in solution. Under these conditions the probabilities of hydrolysis of any acetyl groups in one molecule will be similar to the reaction probabilities of these groups in another molecule and products with a reasonably even degree of substitution less than three may be obtained. 

The acetyl group in aconitine may be eliminated in two other ways (a) by heating aconitine in sealed tubes with methyl alcohol, when methylbenzoylaconine, m.p. 210-1°, is formed, or (b) by heating the alkaloid at its melting-point, when pyraconitine, C32H43O9N, m.p. 167-5° (171°, Schulze), [a] ° — 112-2° (EtOH), is formed. The latter yields crystalline, laevorotatory salts, and on hydrolysis by alkalis affords benzoic acid and pyraconine, C2sH3gOgN, amorphous, [a]n — 91° (HgO), but yields a crystalline hydrochloride, B. HCl. 2-5H20, m.p. 154° (135°, Schulze), Md - 102° (HgO) (- 124-6°, Schulze). ... 

Hydrolysis removes the acetyl group from nitrogen and converts the two ester functions to carboxyl groups. Decarboxylation gives the desired product. 

Acylation of thiosemicarbazide with propionyl chloride, interestingly, does not stop at the acylated product (124). Instead, this intermediate cyclizes to the thiadiazole, 125, under the reaction conditions. Hydrolysis then affords the heterocyclic amine, 126. Acylation by 88 followed by removal qf the acetyl group affords sulfaethidole (116) variation of thle acid chloride used in the preparation of the heterocycle leads to 117 and 118. 

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