Oxirane/carbon dioxide

Studies of the regioselectivity of oxirane/carbon dioxide copolymerisation showed the polar effect exerted by the ring substituent, but not the bulkiness, to be the factor determining the direction of ring opening [231,232]. In the case of propylene oxide/carbon dioxide copolymerisation, C g—O bond cleavage... 

A concerted mechanism of oxirane/carbon dioxide copolymerisation with catalysts formed in diethylzinc-dihydric phenol systems and related systems has been proposed [76,206,207], According to this mechanism, the oxirane coordination and enchainment occur as shown by the following scheme ... 

At the end of considerations dealing with oxirane/carbon dioxide copolymerisation, copolymerisation run under supercritical conditions in carbon dioxide as the reaction medium should be mentioned [239]. 

As regards oxirane/carbon dioxide copolymerisation with (dmca) A1C1, it yields low molecular weight propylene oxide/carbon dioxide copolymers with a prevailing content of ether linkages as well as cyclohexene oxide/carbon dioxide copolymers of predominantly carbonate linkages. 

It is interesting that the reaction in the oxirane-carbon dioxide tetrahydro-furan system with (dmca)AlCl produced the respective terpolymer, especially when cyclohexene oxide was used as the oxirane. The cyclohexene oxide tetrahydrofuran-carbon dioxide terpolymer appeared to contain up to 29mol.-% carbon dioxide and 20mol.-% tetrahydrofuran units [244]. 

Taking the above into account, oxirane-carbon dioxide-tetrahydrofuran terpolymerisation should be considered to involve active sites that change in nature as the reaction progresses an account of cross-propagation, like those appearing and disappearing in schemes (6) and (7) [41,74,244],... 

Subsequent reactions with n-octyl bromide, c-hexyl bromide, bromoacetaldehyde diethylacetal, benzyl chloride, oxirane, carbon dioxide, carbon disulfide (followed by reaction with methyl iodide), and methyl isothiocyanate. 

Figure 10 Alternating (butoxymethyl)oxirane/carbon dioxide polymer...

Copolymers of carbon monoxide, carbon dioxide, sulfur dioxide or carbon disulfide are frequently formed in combination with oxiranes, thiiranes or aziridines. Copolymerization of carbon monoxide and ethylenimine was carried out under radiation and the formation of 3-nylon was observed238. ... 

Besides protonation, a variety of other electrophiles have been employed for the trapping of allenyllithium intermediates 105, e.g. aldehydes and ketones, oxiranes and carbon dioxide [69]. Scheme 2.38 shows a selection of functionalized allenes obtained by this method. 

Yields are variable, but the reaction appears to be promoted by the presence of alkoxymethyl substituents on the oxirane ring. Reactions with p-propiolactones give lower yields (<10%). Cyclic carbonates can also be obtained from the zinc(II) promoted reaction of oxiranes with carbon dioxide [62] the stereochemistry of substituents on the oxirane are retained in the carbonate. 

Kruper WJ, Swart DJ (1985) Carbon dioxide oxirane copolymers prepared using double metal cyanide complexes. US Patent 4500704... 

Metallated polystyrenes are versatile intermediates for the preparation of a number of polystyrene derivatives. Metallated polystyrene has been prepared from haloge-nated polystyrenes by halogen-metal exchange [41,42,65,66] and by direct metallation of polystyrene [67-69] (see Chapter 4). Electrophiles suitable for the derivatization of metallated polystyrene include carbon dioxide, carbonyl compounds, sulfur, trimethyl borate, isocyanates, chlorosilanes, alkyl bromides, chlorodiphenylphosphine, DMF, oxirane, selenium [70], dimethyldiselenide [71], organotin halides [69], oxygen [72], etc. [41,42,65-67],... 

Although propylene oxide has been the oxirane most widely studied in copolymerisation with carbon dioxide, there are a variety of other oxiranes capable of coordination copolymerisation with carbon dioxide (Table 9.4). 

Copolymerisation of propylene oxide as well as other oxiranes with carbon dioxide in the presence of zinc-based coordination catalysts is generally accompanied with the formation of a cyclic five-membered carbonate, propylene carbonate or another alkylene carbonate [147,206,207,210,212,230]. The alky-lene carbonate, however, is not the precursor for poly(alkylene carbonate), since it hardly undergoes a polymerisation under the given conditions [142-146],... 

Styryl carbanions readily react with carbon dioxide 31) to yield carboxy end groups. These terminal groups are also introduced by reaction with anhydrides 19) whereas the use of oxirane 23) leads to the formation of hydroxy end groups esters and nitriles are used to introduce carbonyl functions at the chain end. These reactions can be carried out at low temperature in THF solution and proceed quantitatively if no deactivation by protons occurs. 

The synthesis of carbamic esters of 1,2-diols has been achieved by reacting oxiranes and amines in an atmosphere of carbon dioxide under various experimental conditions. ... 

The 4,5-corane (84) is obtained in SOX yield on photo-decarbonylation of the pentacyclic ketone (85). Photochemical decomposition of the carbonate (86), by the loss of carbon dioxide, affords a mixture of products containing oxirane. styrene oxide, bibenzyl and phenylacetaldehyde. Triplet sensitized irradiation yields products solely from benzyl radicals. - An earlier study of the irradiation (at 254 nm) of the carbonate (87) reported that benzaldehyde, phenyl carbene, and carbon dioxide were produced. A reinvestigation of the irradiation of this compound (at 254 nm in acetonitrile) has provided evidence that the cis- and trans-stilbene oxides (88) and (89) are formed as well as deoxybenzoin and smaller amounts of diphenylacetaldehyde and bibenzyl. When methanol is used as the solvent the same products are produced accompanied by benzylmethyl ether, 1,2-diphenylethanol, and 2,2-diphenylethanol. These authors suggest that the oxiranes (88) and (89) are formed by way of... 

The synthesis of 5-membered cyclic carbonates is carried out by the reaction of oxirane with carbon dioxide in the presence of various quartemary ammonium salts catalyst as shown in Scheme 1 and their results are listed in Table 1. 

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