Anhydrid, acetic nitrous

An observation which is relevant to the nitration of very reactive compounds in these media ( 5.3.3) is that mixtures of nitric acid and acetic anhydride develop nitrous acid on standing. In a solution ([HNO3] = 0-7 mol 1 ) at 25 °C the concentration of nitrous acid is... 

Phenyl isothiocyanate has been prepared from thiocarbanilide by the action of phosphorus pentoxide, hydrochloric acid, iodine, phosphoric acid, acetic anhydride, and nitrous acid. It has also been prepared from ammonium phenyl dithiocarbamate by the action of ethyl chlorocarbonate, copper sulfate lead carbonate, lead nitrate, ferrous sulfate,and zinc sulfate. ... 

Carbon monoxide bears the same relation to formic acid that sulfur trioxide bears to sulfuric acid, or that platinic chloride bears to chlorplatinic acid, etc. Carbon monoxide also bears the same relation to the higher organic acids such as acetic, propionic, etc., acids that sulfur dioxide bears to the sulfonic acids, or that the anhydride of nitrous acid bears to the nitro compounds, etc. 

Amino groups are acetylated normally and are converted to hydroxy compounds with nitrous acid. Tlie 2,3-diamino [2,3-f>] derivative gives an imidazolo fused pyridopyrazine with acetic anhydride (75USP3898216). The oxidative removal of hydrazino groups has been used to give ring-unsubstituted derivatives (79JHC305). 

Semicarbazones are prepared in high yields from A " -3-ketones. However, regeneration of the parent dienone is usually difficult and inefficient and very low yields are usually obtained on hydrolysis by nitrous acid, hydrochloric acid or acetic anhydride-pyridine. " In some examples higher yields have been obtained with aqueous acetic acid. ... 

Among the NO-donor mesoinoic heterocycles, the sydnonimines have attracted by far the most interest. They were first obtained by Brookes et al. [78] and Kato et al. [79] by the action of nitrous fumes on a-( N-rnelh yl-N-riilrosoamino)-nitriles followed by the action of acetic anhydride. Whereas sydnones represent a family of stable heterocycles, sydnonimines, with the exception of 3-hydroxysydnonimine (81, R=OH, Ri =H) that forms an inner salt [80], are unstable if not protonated to a salt or acylated to stable N-acylimino derivatives. In this case they can be stored at room temperature... 

Nitration of the aromatic ring of (223) occurs at the 7-position. However, its reaction with fuming nitric acid in acetic anhydride followed by treatment with methanol gave the 5-methoxy-4-nitro derivative. This product, on treatment with triethylamine, eliminated nitrous acid from the 3,4-positions. 

The primary aromatic amines are most readily estimated by means of nitrous acid (see p. 493). Primary or secondary amines, either alone or in presence of tertiary amines, may be estimated by acetylation, since the last do not react. About 1 gm. of the substance or mixture is weighed into a small flask provided with a reflux air condenser, and 5 c.cs. of acetic anhydride added from a pipette having a soda-lime guard tube. In another flask, also provided with a similar condenser, 5 c.cs. acetic anhydride are placed. The two flasks are allowed to stand at room temperature for 30 minutes to 1 hour, after which time 50 c.cs. of water are added to each, and both are placed on the steam bath for an hour in order to convert the remaining acetic anhydride into acetic acid. After cooling, the amount of acetic acid in each flask is titrated with standard sodium hydroxide or standard baryta, using phenolphthalein as indicator. The difference in the two titrations corresponds to the amount of primary or secondary amine present. 

Anagnostopoulos found that the amino group reagents ketene, nitrous acid, formaldehyde, and phenyl isocyanate all inactivated bovine liver and kidney phosphatases 102). On the other hand, acetylation of chicken intestinal phosphatase with acetic anhydride gave an active product with optimum activity more alkaline than normal 103). The enzyme preparation was impure and acetylation only 70% complete... 

Acylaminomalonic esters and related reagents are widely used for the synthesis of a-amino acids. The method differs from those syntheses already discussed in that the amino group is incorporated into the system from the outset. A popular reagent is diethyl acetamidomalonate (35). The acetamido group can readily be introduced into the reactive methylene position in diethyl malonate by first converting the latter into the hydroxy-imino derivative (33) by reaction with nitrous acid or an alkyl nitrite (cf. Section 4.2.7, p. 413). This derivative is then reduced catalytically to diethyl aminomalonate (34) which is acetylated using acetic anhydride. 

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