| Popis: |
The reaction of bromine with a variety of dimethyl acetals at − 60° in sulfur dioxide is described. Electrophilic attack of bromine on oxygen leads to methyl hypobromite (CH3OBr) together with mono methoxycarbenium bromide or - depending on the stability of the cation - its covalent counterpart, the α-bromo-ether. The reaction is catalysed by acids. Acetals derived from linear and cyclic carbonyl compounds react in this way with one exception: with 1,1-dimethoxycyclopropane, the acetal of cyclopropanone, electrophilic attack by bromine is not on oxygen, but on the cyclopropane ring. Ring rupture leads to a relatively stable di methoxycarbenium ion. |
