chloral hydrate synthesis

If this works it would be a very useful reaction indeed as chloral hydrate is almost unobtainable these days and yet still a usefull organic intermediate for the synthesis of substituted isatins. Do you have a reference for this reaction or did you discover it yourself? If the later do you have some more data on the characterisation of the product other than "odor reminiscent of chlorbutanol" since I don´t know what chlorobutanol smells like.

A few more details and some pictures would be nice too

My interest in this reaction is that I have done quite a few experiments on the oxidation of ethylene in an attempt to produce oxidative dimerisation. There are two published procedures that I know of, one in Japanese which does not appear to be available digitally and one in from J Org Chem. Both of these procedures use benzoyl peroxide to oxidize the trichloroethylene to a mixture of hexachlorobutene (main product C4H2Cl6), pentachlorobutadiene (minor product C4HCl5) and traces of 1,2,3,4-tetrachloronaphthalene.

The alkaline nature of bleach could remove HCl from the trichloroethylene to yield 1,2-dichloroacetylene as described in one of Woelens threads and then this could suffer chlorination by free chlorine produced by the break down of free hypochlorous acid as the mixture is acidified to give tetrachloroethylene and finally hexachloroethane. As you can see there are many possible products of this reaction.

I have tried oxidizing trichloroethylene with sulphur at reflux temperatures but this reaction is very slow and almost all of the starting solvent was recovered. with iodine and barium carbonate (the later compound to absorb the HI that might be produced before it could add across the ethylenic bound. Curiously in this latter reaction I could find no evidence that the free iodine added to the double bond either, it seems remarkably unreactive.

[Edited on 18-4-2015 by Boffis]

Quote: Originally posted by HgDinis25

Please provide references. How did you find this out? I can't think of way/mechanism for this reaction to work.

Synthesis of Chloral Hydrate

Since I needed chloral hydrate for a future synthesis, and I really didn't want to have to deal with large amounts of Cl2 gas, as well as seeing as the previous user didn't seem to document their attempt, I decided to have a crack at this. So here is my short write up:

Firstly, I needed a source of trichloroethylene as it is a lot harder to find these days. I managed to find a source in a product called "CRC Heavy Duty Degreaser" for about $20 USD, including shipping. MSDS states about 90% Trichloroethylene (and the rest, propellants), and each bottle contains about a pound of product.

Using the flimsy straw that came with the can, I sprayed out and measured 87.6 grams of the trichloroethylene(TCE), which according to my math, is 60mL.

I then measured out the rest of the reactants, as according to @erich_zurich; 375mL of 8.5% NaClO solution(although mine is old so I expected it to be less concentrated), as well as 250mL of 5% vinegar.

I then added the NaClO solution to a 1L beaker, followed by the TCE. Finally, the acetic acid went in, with no noticeable Cl2 release. The mixture was stirred by hand, rapidly to allow for good mixing. The beaker was then placed in a small cooler outside with the lid slightly ajar to allow for any possible Cl2 released to escape.

After two hours, I went to stir the mixture, and to my surprise, the bottom TCE layer had taken up most of the yellow color of the solution, and a very light underlying smell of chlorine could be detected.


I stirred the mixture occasionally throughout the next 48 hours, and on the second day, the mixture had gone nearly colorless, yet the smell of Cl2 remained.


On the third day, the solution remained the same color, but almost no Cl2 could be detected, and the mixture had taken up a medicinal smell, to my hope.

I decanted the aqueous layer into a separate container, and collected the bottom layer in a separatory funnel. I set aside this layer in a beaker to evaporate over a fan and an open window, while, thanks to a few who suggested this, I worked up the aqueous layer by adding 100mL of diethyl ether and stirred vigorously, in order to try to extract any product that may be dissolved. I separated the ether as well and allowed that to evaporate, but to no avail; almost nothing crystallized out of the solution.

After the TCE solution had all evaporated away, I was happily left with some white moist crystals left in the beaker, that smelled strongly medicinal. I scraped these into a container and weighed the product.


I was left with 5.59g of chloral hydrate, which was much lower than I expected. Though, I am satisfied with this as it is enough to proceed with the next steps in the synth.

I presume the reason for the low yield is possibly the older bleach, but mainly the fact that the product is extremely soluble in water, and there's a LOT of water left over. I presume using newer bleach or calcium hypochlorite and glacial acetic acid would significantly increase the yield.

All in all, this is a much easier way of obtaining CH (besides locating a source of TCE) and a neat way at that.

[Edited on 1/23/2021 by Velzee]



[Edited on 1/24/2021 by Velzee]

Quote: Originally posted by Tsjerk

Nice! DDT for everyone!

Quote: Originally posted by Boffis

Nice work Velzee! Good to see sometime else trying out some of the old claims. Roughly how much of the TCE do you estimate had reacted? I am wondering if it would be possible to distill off some of the unreacted TCE and recycle it into another batch and then work up the residue in order to improve the yield. By the way please could you embed your images into the report so that they are always there. We have so many older threads on SM where the illustrations are now just broken links.

Quote: Originally posted by Tsjerk

Chloral forms a 7% azeotrope with water, so you could distill part of the water layer to concentrate the chloral. https://en.wikipedia.org/wiki/Azeotrope_tables [Edited on 24-1-2021 by Tsjerk]

Quote: Originally posted by Tsjerk

Chloral forms a 7% azeotrope with water, so you could distill part of the water layer to concentrate the chloral. https://en.wikipedia.org/wiki/Azeotrope_tables [Edited on 24-1-2021 by Tsjerk]

Quote: Originally posted by Tsjerk

Trichlorethylen is being replaced by tetrachloroethylene, so they probably changed their formula. [Edited on 12-2-2021 by Tsjerk]