tert-butyl hypochlorite is a useful oxidant due to its solubility in organic solvents and versatility. It is worth having in the toolkit as it mediates radical chlorination without the need for Cl2 gas, and transforms various functional groups. For instance, it converts alcohols to ketones, aldehydes to acid chlorides, carboxylic acids to alkyl chlorides, amines to azo compounds, and sulfides to sulfoxides.[1] Although the compound can be purchased from some chemical vendors (TCI, Fischer Scientific), its large-scale preparation is simple enough to be worth making in-house. It is completely based on a 1969 Organic Syntheses protocol as shown below.[2]
Procedure:[2] To a one-liter Erlenmeyer flask with magnetic stirring was added 500mL of household bleach solution, which was subsequently cooled below 10degC using an ice bath and continuous stirring. At this point, the lights were turned off, and a solution of tBUOH (37mL, 390mmol) and glacial acetic acid (25mL, 430mmol) was rapidly added. Reaction was stirred with cooling for three minutes, then poured into a one-liter separatory funnel, and the aqueous layer discarded. The organic layer was washed with 50mL of 10% aqueous Na2CO3, 50mL of water, then dried with CaCl2. After filtering off the drying agent, the product was stored in a tinted glass bottle in the fridge.
Notes:
- The bleach I used was the same as that used by the Organic Syntheses submitters and checkers: Proctor and Gamble’s Clorox 5.25% NaOCl solution (Household bleach).
- It is likely that the reaction proceeds via an SN1 mechanism. Addition of glacial acetic acid to bleach solution lowers its highly alkaline pH, protonating the hypochlorite into hypochlorous acid in-situ. The acid then protonates tert-butanol and the protic conditions facilitate the rate-determining formation of tert-butyl carbocation, which is attacked by hypochlorite ion to furnish the product. tert-Butyl hypochlorite, which is too hydrophobic, ultimately separates from the aqueous layer.
- The product obtained from this procedure is pure enough for most purposes and no purification was deemed necessary. There are reports of distillation not improving product purity, and even leading to explosions.[3] In personal experience, I went on to use the unpurified compound in air/moisture-free syntheses of triazolium salts with no issues.
- tert-Butyl hypochlorite is one of a few stable organic hypochlorites.[4] It is light-sensitive and thus care should be taken to protect it from direct sources of light, lest it exothermically decomposes to methyl chloride and acetone. It should be kept away from rubber, since violent reactivity occurs.
[1] Simpkins, N. S.; Cha, J. K. t-Butyl Hypochlorite. EROS, 2006. DOI: 10.1002/047084289X.rb388.pub2.
[2] Mintz, M. J.; Walling, C. t-Butyl Hypochlorite. Org. Synth. 1969, 49, 9. DOI: 10.15227/orgsyn.049.0009.
[3] a) Bradshaw, C. P.; Nechvatal, A. Proc. Chem. Soc. 1963, 213. b) Stimson, V. R. Aust. J. Chem. 1965, 18, 126-127.
[4] a) Taylor, M. C.; MacMullin, R. B.; Gammal, C. A. Hypochlorous acid and the alkyl hypochlorites. J. Am. Chem. Soc. 1925, 47, 2, 395-403. b) Priestley, I.; Young, L.; Mullins, R.; Brown, P. The thermal stability of alkyl hypochlorites. IChemE Symposium Series no. 156, 2011, 80-88.