prov:value
| - having the formula N???(Ra Rb Rc Rd)4 An.sup.??? in which Ra, Rb, Rc and Rd are the same or different, and each is C1 -C6 alkyl, especially methyl or ethyl, or each is 2-hydroxyethyl, or one of Ra, Rb, Rc and Rd is benzyl, and the other three of Ra, Rb Rc and Rd are C1 -C6 alkyl, especially methyl or ethyl, and An.sup.??? is a halide ion, especially chloride or bromide, hydroxyl or sulphate.
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