Acetylation acid-catalysed

A further observation is the fact that differences in rates of nitration between the reagents prepared at different temperatures tended to zero as the water concentration of the added nitric acid was decreased to zero73. It has been argued that, since the acid-catalysed hydrolysis of acetic anhydride must be very rapid at 25 °C and removes water which initially competes with acetic anhydride and acetyl nitrate for protons, this removal permits equilibria (30) and (31) to be displaced towards products. The more anhydrous the nitric acid, the less important is this initial hydrolysis of the acetic anhydride and so the difference in the nitrating power of the differently prepared mixtures becomes less. When reagents are mixed at low temperatures, the hydrolysis of the anhydride is very slow, but once this is accomplished, formation of the protonated acetyl nitrate and subsequent nitration is rapid as observed73. 

IV-acetoxy-lV-acetyl arylamines, 39 IV-acetoxy-lV-alkoxybenzamides, 59 acid-catalysed solvolysis of, 65r acid independent and uncatalysed solvolysis of, 611... 

Aryl glycosides of 2-amino-2-deoxy sugars, as might be expected, can be prepared by similar techniques as was illustrated by the synthesis of phenyl 3,4,6-tri-0-acetyl-2-acetamido-2-deoxy-p-D-glucoside and -D-galactoside by toluene -sulphonic acid catalysed reactions between phenol and the hexosamine penta-acetates These products were then anomerised using zinc chloride as catalyst to provide means of obtaining -anomers. 

Bevan and Hudson86 have reported that the hydrolysis of benzoyl fluoride is acid-catalysed and follows the [H30+], whereas other unhindered benzoyl halides do not. A parallel situation is found with the benzyl fluoride and chloride. Satchell87 has likewise demonstrated the hydrolysis of acetyl fluoride and chloride to be acid-catalysed. 

N. E. Byramova, M. V. Ovchinnikov, L. V. Backinowsky, and N. K. Kochetkov, Selective removal of O-acetyl groups in the presence of O-benzoyl groups by acid-catalysed methanol-ysis, Carbohydr. Res., 124 (1983) c8-cll. 

V. A. Timoshchuk, Transformation of uronic acids catalysed boron trifluoride etherate. Synthesis of 4-O-acetyl-1,2-isopropy lidene-3-O-toluene-p-sulphonyl-a-D-xylopyranurono-5,1-lactone, Carbohydr. Res., 145 (1985) 131-134. 

P. A. McNicholas, M. Batley, and J. W. Redmond, Synthesis of methyl pyranosides and furanosides of 3-deoxy-D-marcrco-oct-2-ulosonic acid (KDO) by acid-catalysed solvolysis of the acetylated derivatives, Carbohydr. Res., 146 (1986) 219-231. 

We wish to report that on treatment with a solution of sodium hydroxide in aqueous dioxan, (A) was converted by endocyclic P-0 cleavage into (C). Alkylation of (C) with methyl iodide followed by acetylation with acetic anhydride/pyridine resulted in (D), which reacted with a dilute solution of anhydrous hydrogen chloride in methanol to give R-(+)-ethyl 0,S-dimethyl phosphoro-thioate (E). Since both S-alkylation and O-acetylation involve no reaction at phosphorus, and available evidence suggests that under the conditions used acid catalysed P-N cleavage in N,N-dialkyl phosphoramidothioates occurs with inversion (6), the observed sequence (Scheme 2) implies that endocyclic P-0 cleavage occurs with retention of configuration at phosphorus. 

Fries rearrangement and phenol acetylation The Fries rearrangement is the acid catalysed transformation of aryl esters into hydroxyarylketones. Both this rearrangement and the two-step transformation (esterification, Fries rearrangement) in one-pot operation of phenols with carboxylic acid or anhydrides will be examined hereafter. Most studies in which acid zeolites were used as catalysts (Tables 3.6 and 3.7) deal with the synthesis of o- and p-hydroxyacetophenones (o- and p-HAP) either by the Fries rearrangement of phenyl acetate [Reaction (3.5)] ... 

The biological effect of (-)-HCA stems from the inhibition of extramitochondrial cleavage of citrate to oxaloacetate and acetyl-CoA catalysed by ATPicitrate lyase. This limits the availability of acetyl-CoA units required for fatty acid synthesis and lipogenesis (Sullivan, 1984). The inhibition of ATP cit-rate lyase by (-)-HCA leads to less dietary carbohydrate utilization for the synthesis of fatty acids, resulting in more glycogen storage in the liver and muscles. Many in vitro... 

A new alkaloid, holacetine (la), has been isolated in 0.04% yield from the root bark of Holarrhena antidysenterica, together with the known component cones-sine.1 Acetylation of holacetine gave an O-acetyl derivative (lb), vigorous acid-catalysed hydrolysis of which yielded the (20S)-20-amino-pregnane (lc). The identity of the latter, and hence of holacetine, was established by its conversion via standard methods into the known alkaloid funtumafrine C (2), and by its preparation from (20S)-3/3-hydroxypregn-5-ene-20-carboxylic acid.1 Conessine has been identified in tissue cultures of H. antidysenterica.2... 

We met cellulose, the bulk polysaccharide of woody plants, in Chapter 49. It is a strong and flexible polymer but no use for making fabrics or films as it cannot be processed. One solution to this problem is to carry out chemical reactions that transform its properties. Acid-catalysed acetylation with acetic anhydride gives a triacetate with most of the free OH groups converted into esters. 

The starting material for this process is wood pulp, cloth, or paper waste and the acetic acid is added first to swell the material and allow it to take up the reagents better. Organic solvents often do this to polymers. The anhydride now carries out the acid-catalysed acetylation and the cellulose triacetate, unlike the cellulose, dissolves in the reaction mixture. The new polymer is often known simply as acetate . 

Increased steric hindrance in the 9a -methyl-11 -oxo-oestrone derivative (137) does not prevent attack by methylmagnesium bromide to give the 9a, 1 la-dimethyl-11/3-alcohol (138), opening the way to novel patterns of substitution in ring C (Scheme 3).143 The acid-catalysed dehydration of the 11/3-alcohol (138) with rearrangement is noteworthy, giving the novel ll,ll-dimethyl-8-ene (139). Acetylation of the hindered tertiary alcohol (138) was effected with refluxing acetic... 

The first example of a Friedel-Crafts type reaction in an ionic liquid medium dates back to 1976 when the electrochemical oxidation of hexamethylbenzene in [C2py]Br-AlCl3 afforded a mixture of alkylated polyphenyl compounds.[69] Other early examples include the alkylation of benzene in C2Ciim C1-A1C137 and the acylation of ferrocene in [C2Ciim]I-AlClJ71 There are now numerous examples of Lewis- or Bronsted acid-catalysed Friedel-Crafts type reactions in ionic liquids. These include alkylation,[72 76] acylation,[71,77"83] arylation,[77 841 sulfonylation,[851 sulfoamylation[86] and O-acetylation of alcohols.[87,881... 

It appears that the NO+ group can be transferred directly only to those species which can behave as reasonably powerful nucleophiles in moderately acid solution. This is undoubtedly the reason why species such as azide ion and amines do not appear to act in this way since they are very extensively protonated in these solutions. Azide ion catalysis has been reported in one case, however (Meyer and Williams, to be published) the denitrosation of N-acetyl-N-nitrosotryptophan, which reacts very rapidly, has been examined at pH 6 where a substantial quantity of free azide ion exists. Presumably the same would be true for some amines at these very low acidities. However, there is experimental evidence from two independent groups which shows that a direct (sometimes called trans-) nitrosation by nitrosamines can occur with aromatic amines. The reactions of N-nitrosodiphenylamine in aqueous acid solution were studied in this context (Challis and Osborne, 1973). The reaction was acid-catalysed for all the substrates studied and was believed to involve the protonated form of the nitrosamine (here written as PhjNNO, H" ). Two separate pathways were detected (a) a direct reaction with N-methylaniline (without the formation of free nitrous acid or a derivative of nitrous acid) as outlined in Scheme 20 and b) an indirect reaction with... 

Dawe, R D, Fraser-Reid, B, a-C-glycopyranosides from Lewis acid catalysed condensations of acetylated glycals and enol silanes, J. Chem. Soc., Chem. Commun., 1180-1181, 1981. 

---