Amines acetylations, acetic anhydride

Acetyl derivatives. Primary and secondary amines are best acetylated with acetic anhydride ... 

A Methylanthrapyridone and Its Derivatives. 6-Bromo-3-methylanthrapyridone [81-85-6] (75) is an important iatermediate for manufacturiag dyes soluble ia organic solvents. These solvent dyes are prepared by replacing the bromine atom with various kiads of aromatic amines. 6-Bromo-3-methylanthrapyridone is prepared from 1-methyl amino-4-bromoanthra quin one (43) by acetylation with acetic anhydride followed by ring closure ia alkaU. The startiag material of this route is anthraquiaoae-l-sulfonic acid (16). 

The reactivity of the bromo and amino functions in 4-bromo-l//-3-bcnzazepin-2-amine (8) has been investigated thoroughly.15-41 Acetylation with acetic anhydride at room temperature proceeds normally to give A%icetyl-4-bromo-17/-3-benzazepin-2-amine (72% mp 171 — 173CC), whereas in refluxing acetic anhydride, the diacetyl derivative 9 is produced. In each instance, the acetylated products are isolated by removal of the excess acetic anhydride and crystallization of the residue from a suitable solvent. If, however, the acetylation mixtures are quenched directly with water then only ring-opened products are formed.15... 

The main problem encountered during electrophilic substitution reactions of aromatic amines is that of their veiy high reactivity. Substitution tends to occur at ortho- and para-positions. If we have to prepare monosubstituted aniline derivative, how can the activating effect of -NH group be controlled This can be done by protecting the -NH group by acetylation with acetic anhydride, then carrying out the desired substitution followed by hydrolysis of the substituted amide to the substituted amine. 

The unprotected amine was acetylated with acetic anhydride and the nitrile was converted to the ethyl ester in acidic ethanol with concomitant removal of the Boc group to provide oseltamivir. Finally, salt formation with 85% phosphoric acid in ethanol afforded oseltamivir phosphate (1). 

Imines are formed by condensation of aldehydes or ketones with primary amines, but they form with more difficulty than enamines.84,85 A special case of enamine preparation was described with 20-oxo-steroids.86 Treatment of these ketones with a primary amine gives a 20-ketimine, which is acetylated with acetic anhydride, with migration of the double bond and formation of 20-(A-acetylalkylamino)-J17(20)-pregnene (14) reduction of 14 with lithium aluminum hydride affords the enamine. 

Alcohols, phenols, thiols, and amines can be acetylated with acetic anhydride in the presence of montmorillonite K10 under mild conditions.239 Octyl acetate was obtained in 1 hr from 1-octanol, in 96% yield, using K10 at room temperature. Peracetylation of sugars, such as glucose, has been done in similar fashion in 92-99% yields.240... 

Nitration of the aromatic hydrocarbon is followed by reduction with tin and hydrochloric acid The resulting amine is acetylated with acetic anhydride or benzoylated with benzoyl chloride... 

One of the simplest and most efficient methods of acylation is the treatment of amines (or other nucleophiles) with anhydrides of carboxylic acids. Acetylation with acetic anhydride is common practice and it may seem rather surprising that the analogous reaction has not been used for peptide bond formation from the earliest days of peptide synthesis. One possible explanation for this delay in the acceptance of anhydrides is the wastefulness of the process. Of the two molecules of the carboxylic acid comprised in the molecule of the anhydride only one is incorporated into the product while the other is regenerated but usually not recovered ... 

Reductive amination of aldoses with chiral l-(—)-a-methylbenzylamine in the presence of sodium cyanoborohydride, carried out overnight at room temperature, followed by acetylation with acetic anhydride in pyridine (100°C, Ih) gives diastereoiso-meric l-(N-acetyl-a-methylbenzylamino)-l-deoxyalditol acetates. LC of these derivatives on silica gel permits resolution of enantiomeric pairs, which are detected by UV photometry at 230 nm. 

Aniline (6) is converted to acetanilide (7) by acetylation according to the sequence shown in Equation 21.3. In this reaction, aniline is first converted to its hydrochloride salt 14. Acetic anhydride and sodium acetate are then added to give a mixture in which sodium acetate and 14 are in equilibrium with acetic acid and aniline. As free aniline is produced by this acid-base reaction, it rapidly undergoes acetylation by acetic anhydride to give acetanilide. This particular method for acetylating amines is general, and the yields are usually high. 

Acetylation with acetic anhydride in anhydrous pyridine can be used for the determination of primary and secondary amines according to equations (19) and (20). 

Amino groups have been determined by acetylation with acetic anhydride in dimethylacetamide. Diethylamine was added and the excess amine was titrated potentiometrically [127]. 

Amino groups have also been acetylated with acetic anhydride in dimethylacetamide. Diethylamine was added, and the excess amine was titrated potentiometrically. The sequence distribution of an aromatic polyamide terpolymer prepared under various reaction conditions was determined by nuclear magnetic resonance spectrometry. Infrared spectroscopy and mass spectrometry have been used to estimate the degree of conversion of polyimides, ie. the extent of polyamic acid ring closure. 

The pivotal reagent proved to be nitrotriol 6, which can be readily acetylated with acetic anhydride or benzylated (12) with benzyl chloride. A family of key monomers and cores was derived from ether 12 by replacement of the nitro moiety by denitration-cyanoethylation (Scheme 7), via the method of Ono generated the mononitrile 13 reduction with borane gave amine 14, whereas catalytic reduction generated the trishomobishomotris (15). 

One disadvantage of using acetic anhydride is that with primary amines, traces of the diacctyl compound, RN(COCH3)2, niay be formed the chances of this secondary acetylation are, however, usually remote, and recrystallisation from an aqueous solvent will generally hydrolyse the diacetyl derivative rapidly back to the mono-acetyl compound. 

Some amines, e.g., aniline, can on the other hand be readily acetylated by dissolving them in cold dil. acetic acid and adding acetic anhydride the method is not however general. 

---