Lead tetracetate

Lead tetracetate. Red lead is warmed with acetic acid in the presence of sufficient acetic anhydride to combine with the water formed ... 

Methyl free radicals, generated either by thermolysis of lead tetracetate in acetic acid solution (401) or by radical cleavage of dimethylsulfoxide by H2O2 and iron (II) salts (408), afford 2- and 5-methylthiazole in the proportion of 86 and 14%, respectively, in agreement with the nucleophilic character of alkyl free radicals and the positive charge of the 2-carbon atom of the thiazole (6). 

Perbenzoic acid gave a doubly unsaturated triol monobenzoate. Only two hydroxyl groups could be acetylated, and one was tertiary. The saturated triol reacted with lead tetracetate to give an a glycol. When reacted with chromic acid, it gave a hydroxy lactone. From these observations, Windaus and Gmndmann (11) described the correct stmcture for ergosterol (1). 

Lead tetracetate Acetic acid, lead (4+) salt (8,9) (546-67-8)... 

Witkop applied the lead tetracetate process to opoyohim-bine, and obtained tetradehydroapoyohimbic acid, ... 

To a solution of 6.36 parts of 17(3-hydroxy-17a-methyl-5o -androst-Ten-3-one in 95 parts of acetic acid and 12 parts of water is added 40 parts of lead tetracetate and 0.6 part of osmium tetroxide. This mixture is stored at room temperature for about 24 hours, then is treated with 2 parts of lead tetracetate. Evaporation to dryness at reduced pressure affords a residue, which is extracted with benzene. The benzene extract is washed with water, and extracted with aqueous potassium bicarbonate. The aqueous extract is washed with ether, acidified with dilute sulfuric acid, then extracted with ethyl acetate-benzene. This organic extract is washed with water, dried over anhydrous sodium sulfate, and concentrated to dryness in vacuo. To a solution of the residual crude product in 20 parts of pyridine is added 10 parts of 20% aqueous sodium bisulfite and the mixture is stirred for about 20 minutes at room temperature. 

Potassium permanganate in neutral solution and lead tetracetate give rise, respectively, to the anticipated glycol and to its diacetate. 

The dehydrogenation of dioximes symmetrically substituted (17, R=Ri, Scheme 6.4) with a variety of oxidants, including potassium ferricyanide, halogens, hypohalides, nitric acid, nitrogen dioxides, and lead tetracetate, is a common route to symmetrically substituted furoxans. 

Treatment of 3-rncthyl A-cthoxycarbonyl-5-aryIidcnchydrazono-l//-pyrazolcs 194 with bromine, in the presence of sodium acetate, in acetic acid gives substituted ethyl 3-aryl-7-cthoxycarbonyI-6-rncthyl-1 //-pyrazolo[5,1 -/ -[l,2,4]triazoles 55 (Equation 35) <2002ARK133>. Analogously, the reaction of compounds 194 with lead tetracetate [Pb(OAc)4] in acetic acid also gives l//-pyrazolo[5,l-c][l,2,4]triazoles 55 (unreported yield) (Equation 35) <2002ARK133>. 

It is worth mentioning that in a few cases the (3-elimination of the silyl radical from the a-silyl alkoxyl radical (47) with the formation of corresponding carbonyl derivative was observed [63,64]. Evidently the fate of a-silyl alkoxyl radical depends on the method of radical generation and/or the nature of the substrate. Two examples that delineate the potentialities of this rearrangements are reported in Reactions (5.33) and (5.34). In the former, the 5-exo cyclization of secondary alkyl radical on the carbonyl moiety followed by the radical Brook rearrangement afforded the cyclopentyl silyl ether [65], whereas Reaction (5.34) shows the treatment of an a-silyl alcohol with lead tetracetate to afford the mixed acetyl silyl acetal under mild conditions [63]. 

Under suitable conditions, further oxidation of the coupled products produces isolable dimer cation radicals. Thus treatment of 9-alkylcarbazoles with lead tetracetate in acetic acid-perchloric acid, or with 2,3-dichloro-5,6-dicyano-p-benzoquinone in acetic acid-perchloric acid, or with tris-(p-bromophenyl)ammoniumyl perchlorate in methylene chloride, or with nitrosonium borofluoride in acetonitrile all gave isolable cation radical perchlorates such as 17. These were reducible with aqueous sodium dithi-onite to the corresponding bicarbazoles the dimer cation radicals could be produced again by reoxidation of the dimer using 2,3-dichloro-5,6-dicyano-p-benzoquinone in acid solution. ... 

I. Periodic Acid (HIO4) or Lead Tetracetate (PblOAc) ), Oxidative Cleavage... 

Lassaigne test, 1039, 1040 defects in, 1043 Lead dioxide, 199 Lead tetracetate, 199, 951 Lessing rings, 92 Leuckart reaction, 561, 567 Liebermann nitroso reaction, 649 Light petroleum, purification of, 174 Ligroin, 174 Linseed oil, 445... 

Lead dioxide is widely used as an oxidizing agent in the arts as well as in the laboratory. It reacts with strong bases with the formation of plumbates, M2Pb03 and dissolves in strong acids, presumably forming plumbic salts. It will not react with weaker acids, such as acetic (c/. the preparation of lead tetracetate, synthesis 17). 

Another 200 g. of the product may be obtained from the mother liquor following the directions of Colson.3 The liquid is returned to the original flask, heated to 80°C., with stirring, and a stream of dry chlorine passed into it. When the reaction is complete, the solution is filtered while hot, and the precipitated lead chloride is washed with hot glacial acetic acid. On cooling, lead tetracetate is deposited from the filtrate. This second crop is contaminated with lead chloride and must be recrystallized if a pure material is desired. 

Cupric acetate does not function as a reoxidant at the low temperature generally useful for the olefin arylation reaction. Mercuric acetate is sometimes useful but it may add to the olefins present and complicate the reaction. Lead tetracetate reoxidizes palladium but also causes the formation of acetates by a reaction apparently analogous to the cupric... 

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