| http://www.w3.org/ns/prov#value | - It is also preferred that either one of R1, R2, R3 and R4 be alkyl, especially methyl and the remaining groups be hydrogen. [0084] R1, R2, R3 and R4 may be the same or different. [0085] Illustrative examples of the compound of formula (1) include 1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathiane-2,2-dioxide, 4-methyl-1,3,2-dioxathiolane-2,2-dioxide and 4-ethyl-1,3,2-dioxathiolane-2,2-dioxide.
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