Potassium Hydrogen Sulfate


[7646-93-7]  · HKO4S  · Potassium Hydrogen Sulfate  · (MW 136.18)

(used in the preparation of acetals;1 dehydrating agent2)

Alternate Name: potassium bisulfate.

Physical Data: mp 214 °C; d 2.322 g cm-3.

Solubility: sol water, isopropyl alcohol, acetone.

Form Supplied in: white powder or granules; fused solid.

Purification: crystallized from ethanol.

Handling, Storage, and Precautions: store in a cool dry place; hygroscopic, corrosive; wash thoroughly after repeated handling; causes burns.

Acetalization Reagent.

Isobutyraldehyde is efficiently protected as its acetal with 2-ethylhexanol in the presence of KHSO4 in 93% yield (eq 1).1 KHSO4 is comparable as a catalyst to benzenesulfonic acid in yield and crude product purity and gives a better colored product as compared to the same reaction catalyzed by Sulfuric Acid (see also p-Toluenesulfonic Acid).

Dehydrating Agent.

Dienones can be generated using KHSO4 under acidic conditions. For example, a steroidal tosylate was refluxed for 45 min with KHSO4 in acetic acid to produce the dienone as the major product (eq 2).3 A carotenoid aldehyde has been prepared by dehydrating a monoprotected triol with KHSO4 at 150 °C (eq 3).4 The unsaturated aldehyde was produced in quantitative yield.

Treating aryl alcohols with fused KHSO4 affords the corresponding alkene. For example, m-chlorophenylmethylcarbinol, KHSO4, and a catalytic amount of p-t-butylcatechol under partial vacuum for 6 h gave m-chlorostyrene in 80-83% yield (eq 4).2 Aryl alcohols are also dehydrated when treated with KHSO4 in the presence of Copper powder. For example, treatment of 1-(2-fluorenyl)ethanol with a mixture of KHSO4/Cu followed by sublimation at 180-200 °C for 30 min afforded the corresponding terminal aryl alkene in 31% yield and a coupled product in 17% yield.5 KHSO4 has also been used to prepare butadienes. Dehydration of 4-phenylbut-3-en-2-ol with KHSO4 gave trans-1-phenylbuta-1,3-diene (see also Alumina).6

Pyruvic acid has been prepared by dehydrating tartaric acid with KHSO4 at 210-220 °C (eq 5).7 Key intermediates in the synthesis of branched long chain fatty acids involve the use of KHSO4. For example, treatment of the diol produced from the reaction of methyl n-pentyl ketone with the Grignard complex of but-4-yn-1-ol with KHSO4 followed by catalytic hydrogenation and oxidation afforded 4-methylnonane-1-carboxylic acid (eq 6).8

Dehydrative coupling using KHSO4 has been used in the synthesis of vitamin K1. Thus treatment of 2-methyl-1,4-naphthohydroquinone-1-acetate and phytol with KHSO4 in dioxane for 90 min at 76 °C gave the corresponding allene (eq 7).9 Hydrolysis of this product gave vitamin K1 in 50% overall yield.

KHSO4 can be used to generate ethers. For example, naphthalan has been prepared in 81% yield by heating fused KHSO4 and 1,8-naphthalyl alcohol for 10 min at 120 °C (eq 8).10 Highly selective monoetherification of symmetrical diols has been accomplished by using KHSO4 supported on silica gel. Treating 1,4-butanediol and dihydropyran with a catalytic amount of KHSO4-SiO2 in hexane afforded, after 50 min, 91% yield of monoether and 6% diether.11 This catalyst system also efficiently dehydrates alcohols.12

1. (a) Blaga, A. I.; Pape, R. F.; Chirilã, T. RRC 1978, 23, 581. (b) Stenberg, V. I.; Vesley, G. F.; Kubik, D. JOC 1971, 36, 2550.
2. Overberger, C. G.; Saunders, J. H. OSC 1955, 3, 204.
3. Jagodziñski, J. J.; Gumulka, J.; Szczepek, W. J. T 1981, 37, 1015.
4. Inhoffen, V. H. H.; Siemer, H.; Möhle, K.-D. LA 1954, 585, 126.
5. Minabe, M.; Suzuki, M.; Ooya, T.; Suzuki, K. BCJ 1978, 51, 544.
6. Morimoto, T.; Hirano, M.; Enokida, T.; Isomoto, A.; Hamaguchi, T.; Zhung, X. JCS(P2) 1988, 1531 and references therein.
7. Howard, J. W.; Fraser, W. A. OSC 1941, 1, 475.
8. Leese, C. L.; Raphael, R. A. JCS 1950, 2725.
9. Hirschmann, R.; Miller, R.; Wendler, N. L. JACS 1954, 76, 4592.
10. Weinheimer, A. J.; Kantor, S. W.; Hauser, C. R. JOC 1953, 18, 801.
11. (a) Nishiguchi, T.; Kawamine, K.; Ohtsuka, T. JCS(P1) 1992, 153. (b) Nishiguchi, T.; Kawamine, K. CC 1990, 1766.
12. Nishiguchi, T.; Kamio, C. JCS(P1) 1989, 707.

Mark R. Sivik

Procter & Gamble, Cincinnati, OH, USA

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