Chloroformic esters

Org inic Esters. An unlimited number of organic esters can be prepared by reactions of poly(vinyl alcohol) employing standard synthesis (82,84). Chloroformate esters react with poly(vinyl alcohol) to yield poly(vinyl carbonates) (118). 

Bis(chloroformic esters) condense with diamines to give polyurethanes (60) (see Urethane polymers). 

Acid chlorides are used for the quantitative deterrnination of hydroxyl groups and for acylation of sugars. Industrial appHcations include the formation of the alkyl or aryl carbonates from phosgene (see Carbonic and chloroformic esters) and phosphate esters such as triethyl, triphenyl, tricresyl, and tritolyl phosphates from phosphoms oxychloride. 

The ester is made by adding benzyl alcohol slowly to a preformed solution of phosgene in toluene at 12-16°C, toluene solvent finally being distilled off under vacuum. When discoloured phosgene was used (probably containing iron salts from corrosion of the cylinder), a violent explosion occurred during the distillation phase, presumably involving iron-catalysed decomposition of the chloroformate ester. 

The early use of aqueous potassium hydroxide in acetone for the acetylation and benzoylation of 3-nitrocarbazole using the acid chlorides has been subsequently repeated for the N-acetylation of 3,6-dinitrocarbazole with acetic anhydride, for the N-acetylation, ethoxycarbonylation, 4-fluorobenzoylation, and prop-2-ynoylation of 2-nitrocarbazole and for the methoxy- and ethoxycarbonylation of carbazole itself utilizing the chloroformate esters. 

Decarboxylation of chloroformic esters is greatly catalyzed by dimethylformamide [90]. As indicated in the following equation, an iminium intermediate with contiguous d-a pairs is involved. 

The methyl group at position 5 in triazolopyrimidine 265 reacted with isoamyl nitrite to give the oxime 266, which was dehydrated to the car-bonitrile 267 (89EGP269149). Cyclization of the respective amidoxime 268 with acid chlorides, acid anhydrides, chloroformate esters and o-carboxylic acid esters gave the oxadiazolyl derivatives 269 (90EGP282009) (Scheme 51). 

The esters 35 are obtained by reaction of hydrazides 34 with chloroformate esters or carbonic diesters 3 23 28 42 as previously discussed for the special case of the activated esters (see Section 10.4.2). The amides 36, on the other hand, are formed from hydrazides 34 with isocyanic acid 3,43,44 or with trimethylsilyl isocyanate 42 (Scheme 10). 

Benzoylation of benzoylmethylene triphenylarsorane (20) with benzoyl bromide gave a kinetically controlled acylated product, which on treatment with sodium acetate in chloroform afforded thermodynamically controlled dibenzoylmethylene triphenylarsorane (21) (56). Acylation with carbonic acid anhydride (32, 56), phenylisocyanate (32), or chloroformic ester (32) gave in no case O-acylated product. Similarly, reaction with acetic anhydride afforded l,3-dioxo-l-phenyl-butylidene-(2)-triphenylar-sorane (56). 

It is this equilibrium which renders difficult the explanation of the course of the reactions which take place when metallic sodium or sodium ethoxide and then alkyl or acyl halide are added to these compounds. At first it was thought that the sodio compound formed with acetoacetic ester was CH3.CO.CHNa.COOC2H5, because the reaction with alkyl and acyl halides always yielded a C-derivative, CH3.CO.CHR.COOC2H5. The first example of a different course of reaction was found in the formation of an O-derivative—/3-carhethoxyhydroxycrotonic ester from sodio-acetoacetic ester and chloroformic ester (J. pr., [2], 37, 473 B., 25,1760 A., 277, 64). This could only be explained by assigning an enol formula to the sodium salt—... 

Some of the C-derivative, acetylmalonic ester, is also formed in the chloroformic ester condensation quoted above. In the majority of cases the C-derivative is produced to the exclusion of the O-derivative. For an explanation, see J. pr., [2], 37, 473 see also equation (4), p. 140. 

The original method of preparing diazomethane is as follows. Methyl-urethane, formed by the interaction of methylamine and chloroformic ester, is converted into the nitroso compound by the action of nitrous acid, the latter yielding diazomethane on treatment with alcoholic potash. 

Carboxylic acid chlorides and chloroformate esters add to tetrakis(triphenylphosphine)palladium(0) to form acylpalladium derivatives (equation 42).102 On heating, the acylpalladium complexes can lose carbon monoxide (reversibly). Attempts to employ acid halides in vinylic acylations, therefore, often result in obtaining decarbonylated products (see below). However, there are some exceptions. Acylation may occur when the alkenes are highly reactive and/or in cases where the acylpalladium complexes are resistant to decarbonylation and in situations where intramolecular reactions can form five-membered rings. 

Bisphenol-A is present as the disodium salt in the aqueous phase of the two-phase mixture. Phosgene enters the system and dissolves in the organic phase. It is believed that the reaction between phosgene and bisphenol-A occurs at the organic-aqueous interface to form the monochloroformate—Reaction 1—or bischloroformate—Reaction 2— ester of bisphenol-A. The chloroformate esters that form grow to oligomers by reaction with additional bisphenol-A or by self-condensation —Reactions 3 and 4, respectively. 

The behaviour of sodium ethyl aceto-acetate towards chloracetic ester and chloroformic ester respectively, indicates that the compound exhibits dynamic isomerism because in the first reaction it behaves as though sodium were directly united to carbon, and in the second reaction as though the sodium were united to oxygen ... 

Tertiary benzylamines react with chloroformate esters under acidic conditions to yield the corresponding benzyl chlorides (equation 173)1096. 

The temperature dependence of the rate coefficient was given by the following Arrhenius equation kx = 10(1394 02)exp [(-174,000 2000)/8.3147] s 1. The relative rate ratio isopropyl chloroformate ethyl chloroformate was 160 at 280 °C. The enhanced rate due to an a-substitution was associated with the degree of polarity of the alkyl halides7. Therefore, the transition state for chloroformate ester decomposition must also be polar. The mechanism was believed to involve a cyclic six-membered transition state in which formation of HC1 is assisted, as shown below. 

Carboxylic acids can be activated in situ in a manner mechanistically analogous to chloroformic ester as mixed anhydrides B (Figure 6.14), which are mixed anhydrides of a carboxylic acid and a carbonic acid halfester. As can be seen from Table 6.1, in... 

Thiadiazole S.S -dioxides (336) have been prepared by the cyclization of N-halomethylsulfonyl-amidines and -guanidines (335 Scheme 120) <70JCS(C)1429>. N-chloromethylsulfonyl-isoureas and -isothioureas (337) cyclize in the presence of base and chloroformate esters to yield the related S,S-dioxides (92) which easily undergo chlorinolysis to produce (93 Scheme 121) (see also Scheme 45) (74BSF1580). 

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