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Chlorohydrins using Trichloroisocyanuric acid


Once again on the hunt for articles, here's the latest one of interest... ketones, as has been established elsewhere, such as, can be made from propenylbenzenes via di-halopropenylbenzenes, which are reacted with a solution of base to give the epoxide via the halohydrin.  Obviously, if we can form the halohydrin, this simply jumps into the scheme a step later, which may improve yeilds anyway.  Rhodium has suggested a number of times that bleach+iso could be used to get to MDP2P, although I haven't seen reports of any efforts in this area... of course, that could be due to misuse of TFSE, but anyway... To further the halohydrin --> P2P cause, I think this article would be of interest:

Trichloroisocyanuric Acid as a Cohalogenating Reagent: An Efficient Transformation of Alkenes into Chlorohydrins, beta-Chloroethers and beta-Chloroacetates
Mendonça, G. F., Sanseverino, A. M. and de Mattos, M. C. S., "Synthesis", 2003, 1, 45-48

The preparation of diverse beta-chloroethers, beta-chloroacetates and chlorohydrins is efficiently achieved under mild conditions by reaction of alkenes with trichloroisocyanuric acid (0.34mol equiv) in alcohols (MeOH, EtOH, i-PrOH, t-BuOH), acetic acid or aqueous acetone, respectively.

Just as an aside before I continue, they mention in the article that Trichloroisocyanuric acid is "a stable and inexpensive solid frequently used for swimming-pool disinfection and easily available in pool supply and some hardware stores."  One could almost imagine that this article was written with clandestine application in mind.

Chlorohydrins 2a-e; General Procedure 1
To a stirred solution of the alkene (10 mmol) in acetone-H2O (5:1, 30 mL), was added trichloroisocyanuric acid (790 mg, 3.4 mmol) at r.t. in small portions. After the elapse of the time shown in Table 1 (the termination of the reaction was determined by the color disappearance of a wet iodine-starch test paper treated with an aliquot), CH2Cl2 (20 mL) was added and the resulting solution was treated with aq sat. NaHSO3 solution. The organic layer was washed with H2O and then dried (Na2SO4). After evaporation of the solvent on a rotary evaporator, the product was isolated by radial chromatography on a Chromatrotron®. Some selected spectral data are given below.

According to the table in the article, this method gave styrene chlorohydrin in 78% yeild.  The other method in the article, which uses alcohol or acetic acid rather than acetone, gives the beta-chloroethers or esters, for example giving the methyl ether of styrene chlorohydrin (by using methanol) in 98% yeild.  Whether this could be rearranged directly, or hydrolysed to give the chlorohydrin or even glycol on reasonable yeild is something that could be tried.

Irrespective, I personally feel that the halopropenylbenzene route is viable, and certainly this method is far better than having to deal with bubbling Cl2 gas through a solution, or making Br2 for a reaction... go in situ halogenation!  Of course, it is yet to be determined how yeilds go, but if someone was interested, I think that the slight reduction in yeild might be made up for by the inexpensive and (relatively) SAFE nature of the acid opposed to the pure halogens.

edit: I changed the title - I think it's more accurate now...

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