Carbonate-ester interchanges

The addition of alcohols to form the 3-alkoxypropionates is readily carried out with strongly basic catalyst (25). If the alcohol groups are different, ester interchange gives a mixture of products. Anionic polymerization to oligomeric acrylate esters can be obtained with appropriate control of reaction conditions. The 3-aIkoxypropionates can be cleaved in the presence of acid catalysts to generate acrylates (26). Development of transition-metal catalysts for carbonylation of olefins provides routes to both 3-aIkoxypropionates and 3-acryl-oxypropionates (27,28). Hence these are potential intermediates to acrylates from ethylene and carbon monoxide. 

Alcoholysis (ester interchange) is performed at atmospheric pressure near the boiling point of methanol in carbon steel equipment. Sodium methoxide [124-41 -4] CH ONa, the catalyst, can be prepared in the same reactor by reaction of methanol and metallic sodium, or it can be purchased in methanol solution. Usage is approximately 0.3—1.0 wt % of the triglyceride. 

Like P—O—C linkages, P—O—P linkages are susceptible to hydrolytic degradation. Scrambling or interchange usually occurs for phosphoms oxyesters at temperatures and acidities lower than those required for the carbon esters but greater than those for the sulfur esters. 

It is essential to neutralize any strong acid present before distilling lactic esters otherwise, condensation by ester interchange occurs, with liberation of alcohol and production of polylactic acid, a linear polyester. Other neutralizing agents, such as alkali or alkaline-earth hydroxides or carbonates, doubtless could be used satisfactorily instead of sodium acetate. 

Hydroxymethylation (formaldehyde) of nitro-imidazole 76 affords 77, which is oxidized to aldehyde 78. To prepare the other fragment for this convergent synthesis, reaction of epichlorohydrin with morpholine leads to the aminoepoxide 79, which is reacted with hydrazine to afford 80. Reaction of this substituted hydrazine with dimethyl carbonate affords oxazolinone 81 by sequential ester interchange reactions. Condensation of 81 with aldehyde 78 affords the antitricho-... 

An alkaline catalyst, sodium methoxide, is created in the same reactor as the ester interchange by first adding sodium metal to the methanol before the triglyceride is introduced. The reaction is performed batch by batch in a carbon-steel vessel at atmospheric pressure. The reaction, shown in the top part of Figure 15—2, results in glycerol and three fatty methyl esters. 

Polycarbonates are polyesters of carbonic acid. The most important commercial polycarbonate is that based on 2,2 -bis(4-hydroxyphenyl)propane(bisphenol A) [Freitag et al., 1988 Sehanobish et al., 1996]. It has been synthesized by the reaction of the dihydric phenol with phosgene or by ester interchange with diphenyl carbonate ... 

Another reasonable step that can take place under the reaction conditions is removal of one of the protons on the carbon a to the carbonyl groups in diethyl malonate. However, this reaction does not lead to the product and is an example of an unproductive step. Another unproductive reaction is ester interchange in diethyl malonate. In this case, sodium methoxide would react with the ethyl ester to produce a methyl ester. However, this reaction is inconsequential because methyl and ethyl esters have similar reactivity and the alkyl oxygens with their substituents are lost in the course of the reaction. 

Several approaches were taken. Capillary-column gas chromatography on a vinylation reaction product showed 24 separate peaks present in the hexenyl acetate fraction however, six of the peaks accounted for about 90% of the total sample. Hydrogenation of the reaction mixture (hydrogen over platinum on carbon) reduced the hexenyl acetates to a mixture of three hexyl acetates and thereby greatly simplified determining the position of oxygen substitution with, however, loss of information on olefin position. We tried to synthesize the specific hexenyl acetate isomers by the ester interchange reactions (Reactions 7a, 7b, and 7c). Mixtures of isomers were obtained, but they corresponded to the main components of the vinylation reaction mixture. For example, the main products isolated from the vinylation of hexene-1 corresponded to the products from Reactions 7a and 7b—i.c., vinyl rather than allyl esters. 

Polycarbonates are characterized by the carbonate (-0-COO-) interunit linkage. They may be prepared by interfacial polycondensation of bisphenol A and phosgene in methylene chloride-water mixture. The resulting hydrogen chloride is removed with sodium hydroxide or, in the case of solution polymerization, pyridine is used as the hydrogen chloride scavenger. Polycarbonate may also be made by ester interchange between bisphenol A and diphenyl carbonate. 

Glycol carbonates undei] o ester interchange reactions with dibasic acids ai2—... 

The ester interchange method is carried out between the diphenol and diphenyl carbonate ... 

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