Keten anhydride formation with

Since reaction of wood with acetic anhydride leads to the formation of acetic acid by-product, which must be removed from the wood, there has been some interest in the use of ketene gas for acetylation (Figure 4.4a). Ketene, for reaction with wood, is produced by pyrolysis of diketene. Provided that the wood contains no moisture, no acetic acid by-product is produced. However, ketene presents handling problems it is very toxic and explosive, and it also has a tendency to dimerize. A comprehensive series of studies of ketene-based acetylation has been performed in Latvia and this work has been reviewed by Morozovs etal. (2003). Hardwoods have been found to be more reactive to ketene than softwoods and the optimal temperature for reaction has been determined as 47 °C. Application of vacuum and treatment of wood with ammonia solution has been used to remove the excess ketene. The reaction of wood with liquid diketene was also studied, with a WPG of 35 % being obtained after reaction for 3 hours at 52 °C. 

Formylation of amines and alcohols. Behai,8 discoverer of the reagent, found that it reacts unidirectionally with simple alcohols to produce alkyl formates free from acetates. Hurd et al. J found that acetic-formic anhydride (prepared from formic acid and ketene) reacts quantitatively with aniline to give formanilide. Another study10 established that acetic-formic anhydride mixes endothermally with 2-nitro-2-methyl-l-propanol, exothermally with 2-nitro-2-methyl-l,3-propanediol, and displays no appreciable temperature effect with either 2-nitro-l-butanol or tris-(hydroxymethyl)-nitromethane. Formic esters are favored by avoiding a high reaction temperature and by not using sulfuric acid as catalyst. The mixed anhydride has been used for the preparation of formyl fluoride.11... 

The almost exclusive O-acylation (as opposed to S -alkylation) of salts of monothio- or monoseleno-phosphonic or -phosphinic acids by acetyl chloride or bromide or benzoyl bromide proceeds, as might be expected, with retention of configuration at phosphorus. The formation of monothiodiphosphonates as by-products has been reported, but the use of ketene for acetylation purposes allows a cleaner reaction without anhydride formation . ... 

The anhydride (72) gives quite different products, (73) and (74), with tris(dimethylamino)phosphine to those previously obtained with triethyl phosphite. The formation of (73) and (74) is suggested to involve keten intermediates and an alternative mechanism is proposed for the phosphite reaction. 

The bromination and hydrolysis of ketenes and bisketenes have been studied. The reaction of the bis(ketene) 289 with bromine has yielded the dibromo fumarate derivative 290, whose /r/mr-con figuration has been confirmed by X-ray crystallography (Scheme 41).366 The hydrolysis of the dibromo fumarate derivative 291 first provided the dibromo derivative (5//)-furanone 292. The prolonged reaction with water afforded the maleic anhydride 293. The methanolysis of the dibromo fumarate derivative 290 has resulted in the formation of an isomeric mixture of dimethyl... 

The reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful. An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene. Nitroform is produced industrially via this method in a continuous process in 74 % yield. " The reaction of ethylene with 95-100 % nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane. Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. ... 

Esterification of linalool requires special reaction conditions since it tends to undergo dehydration and cyclization because it is an unsaturated tertiary alcohol. These reactions can be avoided as follows esterification with ketene in the presence of an acidic esterification catalyst below 30 °C results in formation of linalyl acetate without any byproducts [71]. Esterification can be achieved in good yield, with boiling acetic anhydride, whereby the acetic acid is distilled off as it is formed a large excess of acetic anhydride must be maintained by continuous addition of anhydride to the still vessel [34]. Highly pure linalyl acetate can be obtained by transesterification of tert-butyl acetate with linalool in the presence of sodium methylate and by continuous removal of the tert-butanol formed in the process [72]. 

A convenient method for generating ketenes in the absence of salts is the pyrolysis of suitable ketene precursors. The yield of 5 (R = Me) increases to 93% when propionic anhydride is heated to 55CEC (40 min).53 For unsymmetrically substituted dialkyl- or arylalkylketenes, stereoisomeric cyclobutane-1,3-dione mixture formation is the norm with little preference of any one stereoisomer. This point is illustrated in the product ratios 6A/6B summarized in the table. 

Solid Catalysts. Nafion-H is an active catalyst for acylation with aroyl halides and anhydrides.60,61 The reaction is carried out at the boiling point of the aromatic hydrocarbons. Yields with benzoyl chloride using 10-30% Nafion-H for benzene, toluene, and p-xylene are 14%, 85% and 82%, respectively. Attempted acylation with acetyl chloride, however, led to HC1 evolution and ketene formation. Nation resin-silica nanocomposite materials containing a dispersed form of the resin within silica exhibits significantly enhanced activity in Friedel-Crafts acylations.62,63... 

The kinetics of formation of ketene and acetic acid on thermal unimolecular decomposition of acetic anhydride at 750-980 K have been reported and used to reevaluate the Arrhenius equation as k = 10122exp(—145 kJ mol l/RT) s-1 for the temperature range 470-980 K.54 Results of ah initio MO calculations suggest that the reaction proceeds by concerted elimination through a six-centre transition state, with potential barrier height 156 kJ mol-1. 

Acetic formic anhydride has been prepared by the reaction of formic acid with acetic anhydride2 3 and ketene,4,5 and of acetyl chloride with sodium formate.6 The present procedure is essentially that of Muramatsu.6 It is simpler than others previously described and gives better yields. It is easily adapted to the preparation of large quantities, usually with an increase in yield. Acetic formic anhydride is a useful intermediate for the formyl-ation of amines,3,7 amino acids,8,9 and alcohols,2,10 for the synthesis of aldehydes from Grignard reagents,11 and for the preparation of formyl fluoride.12... 

Nafion-H is an effective catalyst for the liquid phase acylation of aromatic hydrocarbons with aroyl chlorides and anhydrides but reactions with acetyl chloride are complicated by concomitant ketene formation. Aliphatic... 

The formation of acrylonitriles from the reaction of dihalogenomethylene-phosphoranes with aroyl cyanides has now been extended to include the use of aliphatic acyl cyanides, although the conditions need to be closely defined. Perfluoroisocyanates with diphenylmethylenetriphenylphosphorane give the expected keten-imines (28) or their rearrangement products (29). Formylation of both reactive and stable ylides has been achieved using the mixed anhydride of formic and acetic acids. ... 

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