Acetic anhydride decomposition

Five internal rotations are restricted in the 8-center transition state however, three bonds (instead of two as in the former cases) are broken. Although this process produces the wrong products, this is not necessarily a serious problem (see below). Transition state estimates of the 4-factors favor the 6-center displacement process although 4-center transition states had formerly been proposed It has been noted that the decomposition rate coefficient reported for acetic anhydride, the product of the methylene diacetate reaction, was an order of magnitude larger than that for methylene diacetate. This seemed to suggest errors in one or both sets of rate data. The problem has been resolved however, from an examination of the thermodynamics of the acetic anhydride decomposition ... 

Dimethyl-2,6-diallyloxyanthra- (acetic anhydride) Decomposition products 0 50... 

Acetylation of the amine may also be effected by boiling with 20 ml. of glacial acetic acid and 14 ml. of acetic anhydride for 15-20 minutes, followed by decomposition of the excess of anhydride with water and, after boiling for 5 minutes, poirring with stirring into about 75 ml. of water the product is appreciably coloured. 

Davies and Warren" found that when 1,4-dimethylnaphthalene was treated with nitric acid in acetic anhydride, and the mixture was quenched after 34 hr, a pale yellow solid with an ultraviolet spectrum similar to that of a-nitro-naphthalene was produced. However, if the mixture was allowed to stand for 5 days, the product was i-methyl-4 nitromethylnaphthalene, in agreement with earlier findings. Davies and Warren suggested that the intermediate was 1,4-dimethyl-5 nitronaphthalene, which underwent acid catalysed rearrangement to the final product. Robinson pointed out that this is improbable, and suggested an alternative structure (iv) for the intermediate, together with a scheme for its formation from an adduct (ill) (analogous to l above) and its subsequent decomposition to the observed product. 

Sulfenamidothiazoles heated in acetic anhydride rearrange to 2-acetamido-5-thiophenoxythicLZoles (337) (Scheme 193) (32, 456, 457). Only decomposition products are found when these conditions are applied to 336 with X=C or methyl. Substitution in the 4-position of the thicLZole ring (R = methyl, phenyl), however, favors the rearrangement (see p. 82). 

Later, fireflv oxyluciferin was successfully synthesi2ed (403. 408) and has been isolated and identified in firefly lanterns (luciola cruaciata) after the lanterns were treated with pyridine and acetic anhydride to prevent decomposition (409). In 1972, Suzuki and Goto firmly established that oxyluciferin is involved in the bioluminescence of firefly lanterns and in the chemiluminescence of firefly luciferin (403. 410).. A. mechanism involving a four-membered ring cyclic peroxide has been proposed for the reaction (406. 411). However, it was not confirmed by 0 -labelinE experiments (412). 

Decomposition Reactions. Minute traces of acetic anhydride are formed when very dry acetic acid is distilled. Without a catalyst, equiUbrium is reached after about 7 h of boiling, but a trace of acid catalyst produces equiUbrium in 20 min. At equiUbrium, about 4.2 mmol of anhydride is present per bter of acetic acid, even at temperatures as low as 80°C (17). Thermolysis of acetic acid occurs at 442°C and 101.3 kPa (1 atm), leading by parallel pathways to methane [72-82-8] and carbon dioxide [124-38-9] and to ketene [463-51-4] and water (18). Both reactions have great industrial significance. 

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

The Acetic Acid Process. Prior to the energy crisis of the 1970s, acetic anhydride was manufactured by thermal decomposition of acetic acid at pressures of 15—20 kPa (2.2—2.9 psi) (22), beginning with the first step ... 

Crocetin is a dicarboxyUc acid that forms brick red rhombs from acetic anhydride that melt with decomposition at about 285°C. It is very sparingly soluble in water and most organic solvents but soluble in pyridine and similar organic bases as well as in dilute sodium hydroxide. 

The chromium trioxide was of 97% purity. Cooling is necessary on dissolving chromium trioxide in acetic anhydride. Caution. Addition of acetic anhydride to solid chromium trioxide has resulted in explosive decompositions. The trioxide should be added in small portions to the cooled anhydride. 

Hydroboration affords an efficient preparation of the 5a-A -system (141, for example) from A" -3-ketones. Reaction with diborane followed by decomposition of the organoboron intermediate with refluxing acetic anhydride gives good yields of olefins. Ketones must be protected, and alcohols are transformed to acetates. A -7-Ketones yield 5oc-A -olefins (for example, 138). 

Olefins may be obtained by elimination from the organoboron intermediates formed from enol derivatives and diborane. " As in the reaction with a,jS-unsaturated ketones (section IX), the conversion is carried out in two parts first formation of the diborane adduct and second, decomposition in refluxing acetic anhydride. 

This cyano-ester is hydrolysed by boiling with concentrated hydrochloric acid with the formationof pentane-ay -tricarboxylic acid, CO H. CH (CHj. CHj. COjH) andiwhen the sodium salt of this acid is heat with acetic anhydride and distilled, decomposition takes place with the formation of 8-ketohexahydrobenzoic acid or cyclohexanone-4-carboxylic acid—... 

During its preparation from fuming nitric acid and acetic anhydride, strict temperature control and rate of addition of anhydride are essential to prevent a runaway violent reaction [1], An explosion occurred during preparation in a steel tank [2], It should not be distilled, as explosive decomposition may occur [1],... 

By thermal decomposition on the surface of a glowing platinum wire, acetic anhydride loses water and is converted into ketene, the unimolecular anhydride of acetic acid (Wilsmore) ... 

In a 3-1., three-necked, round-bottomed flask fitted with a powerful slow-speed stirrer having a Teflon blade, a 500-ml. dropping funnel, and a thermometer arranged to dip into the liquid is placed 588 g. (366 ml., 6 moles) of concentrated sulfuric acid. The flask is surrounded by an ice-salt mixture, the stirrer started, and 1216 g. (1170 ml., 12 moles) of acetic anhydride (Note 1) is added at such a rate that the temperature does not rise above 20° (Note 2). The separatory funnel is removed and 912 g. (6 moles) of coarsely powdered D,L-camphor is added (Note 3). The flask is then closed with a stopper and stirring is continued until the camphor is dissolved. The stirrer is replaced by a stopper, the ice bath allowed to melt, and the mixture left to stand for 36 hours (Note 4). The camphorsulfonic acid is collected on a suction filter and washed with ether (Note 5). After being dried in a vacuum desiccator at room temperature, the nearly white crystalline product weighs 530-580 g. (38-42%). It melts at 202-203° with rapid decomposition and is relatively pure (Note 6). 

Unsubstituted thieno[3,4-6]thiophene (3) (see Litvinov and Fraenkel ), was prepared by Cava and Pollack s method for benzo[c]-thiophene i.e., thermal decomposition of H, 3 -benzo[c]thiophene sulfoxide. By refluxing 4/f,6/f-thieno[3,4-ft]thiophene-2-carboxylic acid 5-oxide (91) with acetic anhydride (the synthesis of dihydrothieno-thiophenes will be described below), Wynberg et a/." obtained the mixed anhydride 92 in 95% yield. Hydrolysis gave thieno[3,4-6]-thiophene-2-carboxylic acid (93) (88%). Decarboxylation of the acid (93) gave thienothiophene 3, unstable at room temperature [Eq. (29)]. 

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