Aqueous reactions pyridine hydroxylates

Poly(methyl 3-(l-oxypyridinyl)siloxane) was synthesized and shown to have catalytic activity in transacylation reactions of carboxylic and phosphoric acid derivatives. 3-(Methyldichlorosilyl)pyridine (1) was made by metallation of 3-bromopyridine with n-BuLi followed by reaction with excess MeSiCl3. 1 was hydrolyzed in aqueous ammonia to give hydroxyl terminated poly(methyl 3-pyridinylsiloxane) (2) which was end-blocked to polymer 3 with (Me3Si)2NH and Me3SiCl. Polymer 3 was N-oxidized with m-ClC6H4C03H to give 4. Species 1-4 were characterized by IR and H NMR spectra. MS of 1 and thermal analysis (DSC and TGA) of 2-4 are discussed. 3-(Trimethylsilyl)-pyridine 1-oxide (6), l,3-dimethyl-l,3-bis-3-(l-oxypyridinyl) disiloxane (7) and 4 were effective catalysts for conversion of benzoyl chloride to benzoic anhydride in CH2Cl2/aqueous NaHCC>3 suspensions and for hydrolysis of diphenyl phosphorochloridate in aqueous NaHCC>3. The latter had a ti/2 of less than 10 min at 23°C. 

A kinetic and product analysis study of the reactions of the three isomeric phenyl-azopyridines (86)-(88) (PAPys) in aqueous sulfuric acid media (30-97 wt% H2SO4) has been reported. The y-isomer (86) afforded a mixture of the hydroxylated product 4-(4-hydroxyphenylazo)pyridine, the reduction products 4-aminophenol and... 

A. 4-Aaetylpyridine oxime. Hydroxyl amine hydrochloride (25.0 g, 0.36 mol) (Note 1) is dissolved in 50 mL of water, and the solution 1s added to 70 mL of 20K aqueous sodium hydroxide in a 500-mL Erlenmeyer flask. To this magnetically stirred solution 1s added at one time 4-acetyl pyridine (36.3 g, 0.30 mol) (Note 2) a precipitate forms rapidly. The reaction mixture is stirred at 0-5°C for 2 hr then the precipitate is collected by suction filtration and washed with 500 mL of cold water. 

The CCl4-HF-SbF5 system developed by Jouannetaud and co-workers and used in the selective fluorination of imines (see Section 5.10.1) can be applied in the oxygenation of ketones and carboxamides as well. The hydroxylation of ketones is selective [Eq. (5.229)], provided that a five- or six-membered cyclic carboxonium ion preventing fluorination is involved.534,659 Fluorination, however, may be a side reaction with product distributions depending on quenching conditions (aqueous Na2CC>3 or HF-pyridine). Similar features are characteristic of the transformation of carboxamides.659... 

Stacey and Turton61 objected to Isbell s mechanism on two counts first, that he did not specify that a proton acceptor must be used to promote the reaction and second, that the orthoacetate intermediate would not be applicable in the conversion which they demonstrated (by absorption spectra data) to take place on treatment with dilute, aqueous sodium hydroxide. (The presence of the proton acceptor seems implicit in Isbell s general description of the process of enolization.) The mechanism of Stacey and Turton is shown in Formulas XXIV to XXVIII it calls for the donation of electrons by pyridine to the incipient, ionic proton at C2 and elimination of acetic acid between C2 and C3 with the formation of the partially acetylated enediol-pyridinium complex. The pyridinium ion is removed by acetic acid. Electronic readjustment results in the elimination of acetic acid from positions 4 and 5. The final step, conversion of XXVII to XXVIII, was not explained. Stacey and Turton considered that with sodium hydroxide the reaction proceeds after deacetylation by a similar mechanism except that hydroxyl groups take the place of acetyl groups. Neither mechanism requires a free hydroxyl group at Cl, a condition considered by Maurer to be essential to kojic acid formation. 

The acid 350 was demethylated with pyridine hydrochloride, then realkylated with benzyl bromide in aqueous potassium hydroxide to give 351. The latter was converted to the diazoketone 352 by the sequential treatment of 351 with oxalyl chloride and etheral diazomethane. Reaction of 352 with concentrated hydrobromic acid gave the bromoketone 353. The latter was reduced with sodium borohydride at pH 8 -9 to yield a mixture of diastere-omeric bromohydrins 354. Protection of the free hydroxyl as a tetrahydro-pyranyl ether and hydrogenolysis of the benzyl residue afforded 355. The phenol 355 was heated under reflux with potassium m/V-butoxide in tert-butyl alcohol for 5 hr to give a 3 1 epimeric mixture of dienone ethers 356 and 357 in about 50% yield. Treatment of this mixture with dilute acid gave the epimeric alcohols 358 and 359. This mixture was oxidized with Jones reagent to afford the diketone 349. 

The reaction does not occur on heating at 310°C for 2 h in the gas phase or in basic medium (e.g., pyridine, aqueous sodium hydroxide) suggesting that the reaction involves the protonation of the double bond. When the hydroxyl group is tertiary, it appears impossible to avoid the competitive dehydration reaction. However, after standing at room temperature for 7 years in a sealed tube, 2-isopropylidene-l-methylcyclobutanol (253) has undergone ring contraction to the extent of 60% (equation 173) " . ... 

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