Dehydrochlorination, acetate

C with low conversion (10—15%) to limit dichloroalkane and trichloroalkane formation. Unreacted paraffin is recycled after distillation and the predominant monochloroalkane is dehydrochlorinated at 300°C over a catalyst such as nickel acetate [373-02-4]. The product is a linear, random, primarily internal olefin. 

Thermal stabilities of modified PVC samples acet-oxylated to varying degrees (reaction temperature 46°C) were determined [45]. Rate of thermal dehydrochlorination at 1% degradation was taken as a measure of thermal stability. The log of the degradation rate is plotted against the acetate content of the polymer in Fig. 2. 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

Photolytic decomposition of diazirine (25) in the presence of ethyl acetate led to the formation of the ester derived carbonyl ylide (26). Trapping of the ylide with diethyl fumarate led to the formation of the dihydrofuran 28, generated by dehydrochlorination of the initial cycloadduct 27. It occurred with a rate constant... 

This method has successfully been applied for the addition of chloro(l-chloro-2,2-dimethylvinyl)carbene — formed from 1,1,2-trichlo o-3,3-dimethylcyclopro-pane by dehydrochlorination and subsequent ring-opening — onto ketene methyl silyl acetals, the products of which are transformed to interesting allenic esters when treated with tetrabutylammonium fluoride [149]. 

In all cases, authors showed that such copolymers are stable only if intramolecular peroxides resulting from ozonization have been preliminary thermally decomposed before the above reactions. Their presence in the polymer backbones leads, in a very short time, to dehydrochlorination reactions and degradation of polymers. These works have been extended to other polymers, such as chlorinated polyethylene, vinyl chloride-vinyl acetate copolymers [127]. 

Uemura and co-workers have demonstrated that reaction of 1,5-cyclooctadiene with antimony pentachloride in carbon tetrachloride at —20 ° leads to a mixture of the epimeric dichloro bicyclo[3.2.1 ]octanes 49 and 50.83 Through dehydrochlorination and Ag+-promoted ionization, a bicyclo[3.3.0]octenyl acetate was produced (Scheme 16). 

An example of a few of these reactions that occur in our environment with several commonly used pesticides is illustrated in Figures 7-11. Fleck (15) has illustrated in Figure 7 that ultraviolet light catalyzes the decomposition of DDT. In the presence of air, one of the decomposition products is 4,4 -dichlorobenzophenone. However, when air is absent, 2,3-dichloro-l,l,4,4-tetrakis-(p-chlorophenyl)-2-butene is formed. This compound, through subsequent oxidation, may be converted into 4,4 -dichlorobenzophenone. In mammals 2,2-bis(p-chloro-phenyl) acetic acid (DDA) has been identified and shown to be excreted in the feces and urine. The mechanism of formation of DDA is believed to be an initial dehydrochlorination to DDE, which is then hydrolyzed to DDA as shown in Figure 8. Mattson et ah (29) found both DDT and DDE in most samples of human fat, and Walker et ah (44) noted low levels of these same compounds in restaurant meals. 

Boron trichloride reacts with an acetal, or with a mixture of an aldehyde and an alcohol, to give a 1-chloroalkyl ether (yields 40-85%). The l-chloroalkyl ethers are of interest because they are dehydrochlorinated by trimethylamine to give vinyl ethers. 

Poly(vinyl halides) - The photocatalysed oxidation of PVC has been undertaken in the presence of titanium dioxide and zinc oxide pigments and the extent of dehydrochlorination measured. Acetic and formic acids were major products along with carbon dioxide. Copper(II) dialkyldithiocarbamate complexes are also sensitisers. Photodegradable PVC has also been developed by grafting with benzophenone chromophores. Plasticised PVC also degrades and discolours on irradiation but this is due mainly to the plasticiser. ... 

Phosgene can also be used to convert acetic acid to its anhydride [92], and the addition of phosgene to propene, followed by treatment with methanol and dehydrochlorination of the ester (see Section 10.1.2) results in the production of methyl methacrylate [1699]. 

A few 6-methylenebicyclo[3.1.0]hex-2-enes have been prepared by dehydrochlorination of a 1-chloro-l-methylcyelopropane (see Section 5.2.2.1.1.1.) with potassium /ert-butoxide in dimethyl sulfoxide, combined with dehydrobromination to an alkenylcyclopropane (see Section 5.2.2.1.1.4.) in the same reaction step. Bromochloroacetals have been prepared from cyclo-pentenone acetals by chloromethylcyclopropanation followed by bromination. Thus, optically active truns-4, 5 -dimethyl-6-methylenespiro[bicyclo[3.1.0]hex-3-ene-2,2 -[l,3]dioxolane] (2) was obtained in 84% overall yield from the corresponding chloroacetal 1. ... 

Further treatment of a methanolic solution of the crude -chloro ketones with sodium acetate gives a,/3-unsaturated ketones by dehydrochlorination. In the case of bicyclic substrates, the overall process corresponds to a ring enlargement. Application of this method to 1,2-bis(siloxy)cyclopropanes provides 1,3-diketones (Table 3, entry 9). ... 

Treatment of l-trimethylsiloxybicyclo[3.1.0]hexanes45 with iron(III) chloride in dimethyl-formamide at 0°C afforded 3-chlorocyclohexanones 46 which were dehydrochlorinated in situ with sodium acetate in methanol to give cyclohexenones 47 in one step. -... 

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