Lead tetra-acetate

VI.37. OXIDATION WITH LEAD TETRA-ACETATE n-BUTYL GLYOXYLATE... 

An interesting application of lead tetra acetate is to the jireparation of the otherwise dilliculty-accessiblo a-butyl glyoxylate (II) by oxidation of di-a-butyl i-tartrate (I) ... 

Place a mixture of 125 ml. of A.R. benzene and 32 -5 g. of di-re-butyl d-tartrate (1) in a 500 ml. three-uccked flask, equipped with a Hershberg stirrer (Section 11,7) and a thermometer. Stir the mixture rapidly and add 58 g. of lead tetra-acetate (Section 11,50,15) in small portions over a period of 20 minutes whilst maintaining the temperature below 30° by occasional cooling with cold water. Continue the stirring for a further 60 minutes. Separate the salts by suction filtration and wash with two... 

Lead dioxide in acetic acid solution gives lead tetra acetate which oxidises hydrogen bromide (and also hydrogen iodide), but has practically no cflFect under the above experimental conditions upon hydrogen chloride. 

Lead tetra-acetate has also been used to cleave acids. The carboxyl group is replaced by halide or acetoxy. 

Like lead tetra acetate, periodic and also cleaves vicinal glycols very smoothly and forms carbonyl compounds. The reaction introduced by Malaprade in 1928 may be represented as ... 

However, unlike lead tetra acetate, it fails to oxidise oxalic acid. Such oxidation reactions are best carried out in aqueous solutions and at room temperatures. 

Glycols are dehydrogenated by lead tetra-acetate Pb (OCO CH3)4, the C—C bond being ruptured. From ethylene glycol two molecules of... 

Experiment.—Add three drops of glycol to a solution of 1 g. of lead tetra-acetate 2 in 40 c.c. of glacial acetic acid. After half an hour destroy excess of the oxidising agent with a little sulphurous acid, precipitate all the lead with sulphuric acid, filter off the lead sulphate and test the filtrate for formaldehyde with fuchsine-sulphurous acid (see p. 214). The red solution becomes blue on adding concentrated hydrochloric acid (cf. p. 214). 

Add 200 g. of red lead In portions to 750 c.c. of pure glacial acetic acid + 20 c.c. of acetic anhydride mechanically stirred and kept at 65°, adding each portion only after the red colour produced by the preceding portion has disappeared. The tetra-acetate crystallises out on cooling. It can be recrystallised from glacial acetic aoid and is stable in the absence of moisture (O. Dimroth and R. Schweizer, Ber., 1923, 56, 1375). For the determination of lead tetra-acetate in solution, see R. Criegee, Ber., 1931, 64, 260. 

Benzilic acid is dehydrogenated by lead tetra-acetate (method of Criegee) giving C02 and benzophenone. Here the acid acts like a glycol. Carry out the experiment in the manner described on p. 117 and isolate the benzophenone by digesting with a little petroleum ether, the oily residue which remains after the glacial acetic acid has been evaporated in a vacuum. 

On treatment with IBD, tetraketones 213 are transformed to pyrones 215. This reaction probably occurs via intermediate cyclic ene-hemiacetal 214. In contrast, lead tetra-acetate (LTA), which generally behaves similarly to IBD, shows a different reactivity pattern in the oxidation of 213, thereby yielding the isomeric pyrone 216 (80TL1575 83JHC1389). 

Oxidation of 1-aminobenzotriazole (283) among other products results in the formation of bistriazolo compound 284. This reaction involves a benzene intermediate and illustrates an example wherein IBD behaves differently than lead tetra-acetate, which in this case gives biphenylene [80JCR(S)303] (Scheme 71). 

Hydrazones 285 are oxidatively cyclized by IBD to form 286. Similar cyclization is accessible by using lead tetra-acetate as an oxidant, but results are inferior to those with IBD [89JCS(P1)543]. 

Hydroxythiazolo[3,2-fi][l,2,4]triazoles (176, R = OH) are also available by this route. Treating 167 with methyl chloroformate (sodium hydroxide) and subsequently with sodium methoxide yields 176 (R = OH) (71GEP1942015 72GEP2032173, 72USP3682943). Thiazolo[3,2-fi][l,2,4] triazoles are also available from 2-aminothiazoles via amidines 178. Lead tetra-acetate dehydrogenation of 178 leads to 179 (94MI1). 

The action of iodine on silver selenoeyanate yields selenocyanogen.3 When potassium selenoeyanate dissolved in anhydrous acetone reacts with a solution of lead tetra-acetate in chloroform, lead selenoeyanate and selenocyanogen result.6... 

The Oxidation of Organic Nitrogen Compounds with Lead Tetra-Acetate J. B. Aylward, Q. Rev., Chem. Soc., 1971, 25, 407-429. 

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