Chlorination-rearrangement

Formation of ketones by bromination (chlorination)-rearrangement of aryl substituted ethylenes (Kakis) (see 1st edition). Conversion of 1-arylalkenes to 2-arylaldehydes with l2 and Ag20 at room temperature, via aryl migration (Kikuchi). 

Acid. The reaction requires only enough acid to generate the ferrous ion which is needed to participate in the first step. Alternatively, a ferrous salt can be added directiy. Generally 0.05 to 0.2 equivalents of either hydrochloric or sulfuric acid is used, but both acids have their drawbacks. Hydrochloric acid can cause the formation of chlorinated amines and sulfuric acid can cause the rearrangement of intermediate aryUiydroxylamines to form hydroxyaryl amines. Occasionally an organic carboxyUc acid such as acetic or formic acid is used when there is a danger of hydrolysis products being formed. 

DAG is treated with ethanol and hydrochloric acid in the presence of inert solvent, eg, chlorinated solvents, hydrocarbons, ketones, etc. The L-ascorbic acid precipitates from the mixture as it forms, minimising its decomposition (69). Cmde L-ascorbic acid is isolated through filtration and purified by recrystallization from water. The pure L-ascorbic acid is isolated, washed with ethanol, and dried. The mother Hquor from the recrystallization step is treated in the usual manner to recover the L-ascorbic acid and ethanol contained in it. The cmde L-ascorbic acid mother Hquor contains solvents and acetone Hberated in the DAG hydrolysis. The solvents are recovered by fractional distillation and recycled. Many solvent systems have been reported for the acid-catalyzed conversion of DAG to L-ascorbic acid (46). Rearrangement solvent systems are used which contain only the necessary amount of water required to give >80% yields of high purity cmde L-ascorbic acid (70). 

Imidazole, 2,4,5-trichloro-1-methyl-chlorination, 5, 398 Imidazole, 2,4,5-trideutero-iodination, 5, 401 Imidazole, 1-trifiuoroacetyl-reactions, 5, 451-452 Imidazole, 2-trifiuoromethyl-hydrolysis, 5, 432 Imidazole, 2,4,5-triiodo-nitration, 5, 396 synthesis, 5, 400 Imidazole, 1,2,4-trimethyl-photolysis, 5, 377 rearrangement, 5, 378 Imidazole, 1,2,5-trimethyl-photochemical rearrangement, 5, 377 rearrangement, 5, 378 Imidazole, 1,4,5-trimethyl-bromination, 5, 399 3-oxide... 

Pyrimido[5,4-c]pyridazin-8-ones chlorination, 3, 345 rearrangement, 3, 345 synthesis, 3, 357... 

Both proton loss and rearrangement reflect the greater positive charge at carbon in a chloronium ion than in a bromonium ion because of the weaker bridging by chlorine. 

Reaction of 1-ethoxycyclohexene (34) with dichlorocarbene gives 1-ethoxy-7,7-dichloronorcarane (35) in 87 % yield. Rearrangement of dichlorocyclo-propane (35) in hot quinoline results in loss of both chlorine atoms to give l-ethoxycyclohepta-l,3,5-triene (37) in 37% yield. Hydrolysis of enol ether (37) with a very small quantity of hydrochloric acid in methanol produces cyclohepta-3,5-dienone (38) in 91 % yield. ... 

In radical reactions not involving bromine or chlorine on the substrate, rearrangements are much rarer One example is the fluorination of di-tert butyl ketone which produces perfluormated / rt-buty isobutyl ketone [J5] Although isolated yields are poor only the rearranged ketone could be isolated This is perhaps only the second example of a 1,2-acyl shift Low fluorine substrate ratios show that this rearrangement occurs after monofluorination... 

Similar preference in replacement by fluorine of tertiary versus secondary and secondary versus primary hydrogens is observed in the fluorination of alkanes with chlorine trifluoride in 1,2-difluorotetrachloroethane at room temperature (Table 3). Skeletal rearrangements accompany the fluorination [31]... 

Another example of a simultaneous chlorine-fluorine exchange and rearrangement IS the reaction of orr/io-methylphenylchloroformate with hydrogen fluoride to give a stable tetrafluorobenzodioxtn [34] (equation 25)... 

Polyhalodiethyl ethers are also formed in the reaction of sulfur tetrafluoride with perhaloacetaldehydes in the case of chloral, a chlorine-fluorine rearrangement occurs [I7Q] (equations 82 and 83). 

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