Acetic anhydride byproducts

Figure 14.8a shows a simplified flowsheet for the manufacture of acetic anhydride as presented by Jeffries. Acetone feed is cracked in a furnace to ketene and the byproduct methane. The methane is used as furnace fuel. A second reactor forms acetic anhydride by the reaction between ketene from the first reaction and acetic acid. 

Eastman uses acetic anhydride primarily for esterification of cellulose, producing acetic acid as a byproduct. This acetic acid is used to convert the methanol into methyl acetate in a reactor-distillation column in which acetic acid and methanol flow countercurrently. 

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

Equally notable is a change in type of by-products when RhCl3 is used as co-catalyst. In Experiments VI-IX both ethylidene diacetate (EDA) and acetic anhydride (AH) are formed as (minor) byproducts. In Experiments I-III not even a trace of these products can be detected and instead alcohols and ethers are co-produced. With RhCls, and in the absence of RUCI3 (Exps. IV, V), EDA and AH are the main reaction products. 

The traditional synthesis of miinchnones involves the cyclodehydration of N-acylamino acids usually with acetic anhydride or another acid anhydride. Potts and Yao (3) were apparently the first to employ dicyclohexylcarbodiimide (DCC) to generate mesoionic heterocycles, including miinchnones. Subsequently, Anderson and Heider (4) discovered that miinchnones can be formed by the cyclodehydration of N-acylamino acids using Ai-ethyl-Ai -dimethylaminopropylcarbodiimide (EDC) or silicon tetrachloride. The advantage of EDC over DCC is that the urea byproduct is water soluble and easily removed, in contrast to dicyclohexylurea formed from DCC. Although the authors conclude that the traditional Huisgen method of acetic anhydride is still the method of choice, these two newer methods are important alternatives. Some examples from the work of Anderson and Heider are shown. The in situ generated miinchnones (not shown) were trapped either with dimethyl acetylenedicarboxylate (DMAD) or ethyl propiolate. 

Assumptions Synthesis of phenylpyruvic acid Batch synthesis process for precursors overal yield of 95+% of theoretical to pheny Ihydantoin overall yield of 90+% of theoretical from phenylhydantoin to phenylpyruvic acid recovery and recycle of acetic acid no byproduct crec taken for acetic acid formed from acetic anhydride addition. Conversion of phenylpyruvic acid and aspartic acid. Bioreactor productivity of-18 g PHE/L/h (four columns in parallel) 98% overall conversion no byproduct credit taken for pymvic acid (recovery cost assumed to be of by revenue from sale) 80% recovery of L-PHE downstream of bioreactor. 

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]. 

Whereas the C2—C4 alcohols are not carboxylated under the usual Koch-Haaf conditions, carboxylation can be achieved in the HF-SbF5 superacid system under extremely mild conditions.400 Moreover, Olah and co-workers401 have shown that even methyl alcohol and dimethyl ether can be carboxylated with the superacidic HF-BF3 system to form methyl acetate and acetic acid. In the carboxylation of methyl alcohol the quantity of acetic acid increased at the expense of methyl acetate with increase in reaction time and temperature. The quantity of the byproduct dimethyl ether, in turn, decreased. Dimethyl ether gave the desired products in about 90% yield at 250°C (90% conversion, catalyst/substrate ratio =1 1, 6h). On the basis of experimental observations, first methyl alcohol is dehydrated to dimethyl ether. Protonated dimethyl ether then reacts with CO to yield methyl acetate [Eq. (5.154)]. The most probable pathway suggested to explain the formation of acetic acid involves the intermediate formation of acetic anhydride through acid-catalyzed ester cleavage without the intervention of CO followed by cleavage with HF [Eq. (5.155)]. 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

The filtrate from this first batch will comprise a solution of 180 to 270 kg of unprecipitated acetylsalicylic acid (1.0 to 1.5 mols), 510 kg of acetic anhydride (5.0 mols), 600 kg of acetic acid (10.0 mols) (obtained as a byproduct in the acetylation step) and 1,200 kg of the diluent toluene. Into this filtrate, at a temperature of 15° to 25°C, ketene gas is now passed through a sparger tube or diffuser plate, with good agitation, until a weight increase of 420.5 kg of ketene (10 mols) occurs. The reaction mixture will now contain 180-270 kg of unprecipitated acetylsalicylic acid (1.0-1.5 mols) and 1,532 kg of acetic anhydride (15 mols) in 1,200 kg of toluene. This mother liquor is recycled to the first step of the process for reaction with another batch of 1,382 kg of salicylic acid. On recirculating the mother liquor, the yield of pure acetylsalicylic acid is 1,780 to 1,795 kg per batch. 

In the ketene process, acetic acid is thermally dehydrated at 750°C to ketene. The ketene is separated from byproduct water and reacted with another mole of acetic acid to produce acetic anhydride. Figure 10.16 is a schematic diagram of this process. 

Of several anhydrides studied, acetic anhydride reacted the most readily. Reactions were carried out by refluxing the wood in a xylene/acetic anhydride solution or with acetic anhydride vapors alone at 120°C. With this system, for each mole of acetate bonded onto the wood a mole of acetic acid is generated as a byproduct. Although this byproduct generation is a disadvantage of the process, the chemical system does penetrate and react quickly with wood, without a catalyst. It is not... 

Neat A-(l -methyl-4-pentenyl)hydroxylamine underwent facile cyclization to the corresponding Y-hydroxypyrrolidine 1 on wanning briefly to 50- 60 °C, via a radical chain reaction involving the nitroxide radical. A-(l-Methyl-5-hexenyl)hydroxylamine cyclized to give A-hydroxypipe-ridine 2 only in refluxing xylene under high dilution conditions, this is necessary to avoid formation of byproducts. The cyclization was facilitated by the presence of a-methyl substituents in the hydroxylamine. Transannular cyclization of A-[(3-cyclohexenyl)methyl]hydroxylamine was not successful. Since the isolation of pure samples of the water-soluble and easily oxidized hydroxylamines was not a satisfactory procedure, the crude reaction mixtures were subjected to reduction with a zinc/acetic acid/acetic anhydride system to isolate acetylated cyclic amines. 

Quinazoline 3-oxide differs markedly from the 1-oxide in its behavior towards anionic reagents. Whereas with quinazoline 1-oxide compounds a substituent is introduced into po.sition 2 or 4 (cf. p 104), in quinazoline 3-oxide ring fission occurs between C2 and N3 in the reaction with acetic anhydride, water, alkali hydroxide, and under the conditions of the Reissert reaction.2 -(Hydroxyiminomethyl)formanilide is also formed as a byproduct in the reaction of quinazoline 3-oxide with active methylene compounds. ... 

Trifluoroacetic anhydride (TFAA) is also a very potent activator for DMSO and concomitant trifluoroacetylation of the starting alcohol is usually not observed [27]. Both the Swem and the TFAA procedure are carried out at low temperature to prevent undesired side reactions, particularly formation of the methylthiomethyl ether. Before these two methods became developed, acetic anhydride was often used for DMSO activation. Flowever, the oxidation under these conditions is slower and the methylthiomethyl ether byproduct is often observed [27]. 

When the Clemmensen reduction was conducted in the presence of acetic anhydride (to trap 4) under anhydrous conditions (1 and zinc amalgam in dry diethyl ether), avoiding an excess of acid (use of a solution of 2 mole equivalents of dry gaseous hydrogen chloride in diethyl ether), acetoxycyclopropanes 7 were obtained in moderate yield. ° At 0-25 °C considerable amounts of 5 and 6 as byproducts render the method synthetically useless. However, careful temperature optimization (preferably — 35 °C) ° completely suppresses their formation. 

Cyclopropanols can be converted to various cyclopropyloxy derivatives (esters, e.g. acetates, ethers, e.g. methyl and ethyl ethers, and acetals, e.g. tetrahydropyran-2-yloxy derivatives) under the appropriate reaction conditions. In most cases the synthesis of cyclopropyl esters by the reaction between a cyclopropanol and an acid chloride (e.g. formation of 1 ) or acetic anhydride (e.g. formation of 2 ) have been reported. The yields were particularly good (84-95%) when acetic anhydride was used, although a drawback of the reaction can be byproduct formation. When a reactive moiety is attached to the cyclopropane ring in addition to the hydroxy group, other reactions can also occur m-l-(aminomethyl)-2,2-dimethyl-3-(2-methylprop-l-enyl)cyclopropanol (3) reacted with phosgene in benzene to give the corresponding carbamate l,l-dimethyl-2-(2-methylprop-l-enyl)-4-oxa-6-azaspiro[2.4]heptan-5-one (4) in 31% yield. ... 

Acetoxyvinylphosphonates are formed as the main products (along with acylphos-phonates as byproducts) in the reactions of dialkyl phosphite with acetic anhydride in MeCN, in the presence of chlorides of transition metals such as iron (II), iron (III) or cobalt. The same chlorides also catalyse the transformation of acylphosphonates into enol acetates by treatment with AC2O in MeCN ... 

This compound, like any nitrile can be catalytically reduced to its corresponding amino compound. To prevent the formation of any byproducts, the nitrile is treated with the catalyst, hydrogen and a mixture of sodium acetate in acetic anhydride. This protects the primary amine and the final product is isolated by alkaline hydrolysis. Summarizing ... 

Which reagent is best can often only be determined by experimentation—commerdaUy, paracetamol is made from para-aminophenol and acetic anhydride largely because the byproduct, acetic add, is easier to handle than HCl. In a retrosynthetic analysis, we don t really want to be bothered by this sort of decision, which is best made later, so it s useful to have a single way of representing the key attributes of alternative reagents. We can depict both anhydride and acyl chloride in this scheme as an idealized reagent —an electrophilic acetyl group MeCO+. 

The second most common process is the methylene chloride system. Methylene chloride, an excellent solvent for cellulose triacetate even at low temperatures, replaces the acetic acid as solvent. Perchloric acid is frequently used as catalyst. Acetic acid is formed as a byproduct of the acetylation therefore, the solvent is a mixture of methylene chloride, acetic anhydride, and acetic acid during and at the end of the acetylation [16]. 

Depending on the reaction conditions, ethylidine diacetate can be the major product of the metal-catalyzed reaction of acetylene with acetic acid and is also a byproduct of the oxidative acylation of ethylene. In addition, ethylidine diacetate is readily prepared by the reaction of acetaldehyde with acetic anhydride (37). A commercial-scale synthesis of vinyl acetate developed and piloted by the Celenese Corporation involved the pyrolysis of ethylidine diacetate obtained from acetaldehyde (38) [219,220]. 

---