Pyridines catalysts

These rate constants are for the hydrolysis of cinnamic anhydride in carbonate buffer, pH 8.45, total buffer concentration 0.024 M, in the presence of the catalysts pyridine, A -methylimidazole (NMIM), or 4-dimethylaminopyridine (DMAP). In the absence of added catalyst, but the presence of buffer, the rate constant was 0.005 24 s . You may assume that only the conjugate base form of each catalyst is catalytically effective. Calculate the catalytic rate constant for the three catalysts. What is the catalytic power of NMIM and of DMAP relative to pyridine ... 

Acyl chlorides are highly reactive acylating agents and react very rapidly with alcohols and other nucleophiles. Preparative procedures often call for use of pyridine as a catalyst. Pyridine catalysis involves initial formation of an acyl pyridinium ion, which then reacts with the alcohol. Pyridine is a better nucleophile than the neutral alcohol, but the acyl pyridinium ion reacts more rapidly with the alcohol than the acyl chloride.103... 

Amount of modifier in mmoles of modifier per gram of catalyst. Pyridine-3-carbonitrile... 

In a first set of experiments [52], the methyl ester of cholic acid 66a (Structures 8) was reacted with diphenylketene (59a) in the presence and in the absence of catalysts [pyridine (50), concave pyridine 3r]. But in all experiments, only the equatorial group in 3-position could be acylated (66b). No functionalization of the axial OH-groups in 7- and 12-position was found (66c, 66d). 

Hydrogenation of pyridines and their benzoderivatives can be carried out with various catalysts. Pyridines are readily hydrogenated to piperidines over Raney nickel at 120°C. The optimal pressure for... 

Anchoring of rhodamine B sulfonylchloride 2. Anchoring the rhodamine dye was carried out under similar conditions as in the preceding paragraph. A suspension of 3-aminopropylsilyl-MCM-41 and 2 in 40 mL dichloromethane was precooled and after 1.5 h an excess of the catalyst pyridine was added. The reaction was finished after 20 h of stirring and the recovered solid extensively washed and subjected to a Soxhlet treatment. 

Carbamates.14 A conventional procedure for preparation of carbamates of secondary alcohols involves reaction with an isocyanate and a basic catalyst (pyridine, triethylamine). Actually, BF3 etherate and A1C13 are generally superior catalysts for this reaction, effected either in benzene or ether (25°, -2 hours). 

Much recent work has been done on the synthesis of pyridines from alkynes and nitriles over cobalt catalysts. For example, 2-vtnylpyndine has heen obtained in good yield from acetylene and acrylonitrile using a cyclopentadienyl-cobalt catalyst. Pyridine has also been obtained from cyclopentadiene and ammonia over a sihca/alumina catalyst. 

Pipendine. the hydrogenation product of pyridine, is used as an intermediate for drugs and for making rubber-vulcanization accelerators, e.g., piperidinium pentamechylenedithiocarbamate (also known as Accelerator 552 ). On a commercial scale, piperidine (hexahydropyridine) is prepared by the catalytic hydrogenation of pyridine, e.g., with nickel catalysts at from 68 to 136 atmospheres pressure and at l50-20C,c,C. or under milder conditions with noble-metal catalysts. Pyridine derivatives can be similarly reduced to substitute piperidines. See formulas below. 

It is interesting that with the rather mild catalyst pyridine hydrochloride, benzene-thiol does not react with saturated ketones, but reacts with a,p-unsaturated ketones to give thioenol ethers (with increased conjugation) or 1,4-additions.35... 

The intermediate in both reactions is a cation but the first (from cyclohexene) adds an anion while the second (from benzene) loses a proton so that the aromatic system can be restored. Notice also that neutral bromine reacts with the alkene but the cationic AICI3 complex is needed for benzene. Another way to produce a more electrophilic source of bromine is to use a pyridine catalyst. Pyridine attacks the bromine molecule producing a cationic bromine compound. 

Fig. 4. The adsorption of pyridine and acetic acid on tin-antimony oxides, (a) Graph showing adsorbed pyridine ( ) and adsorbed acetic acid (O) values as a function of bulk antimony content for catalysts precalcined at 600°C. (b) Variation of the amount of adsorbed pyridine and acetic acid as a function of calcination temperature (°C) of the tin-antimony oxides (O) pyridine adsorption on 6% Sb catalyst (A) pyridine on 19% Sb catalyst ( ) pyridine on 33% Sb catalyst ( + ) pyridine on 64% Sb catalyst ( ) acetic acid adsorption on 6% Sb catalyst (A) acetic acid on 19% Sb catalyst ( ) acetic acid on 33% Sb catalyst (x) acetic acid on 64% Sb catalyst. [Reproduced from J. C. McAteer (7J).]...

Yamazaki, 1971), dictates the correct experimental conditions for POase assays POase is divalently oxidized by peroxide to Compound I, which is, in turn, reduced to the initial state by 2 successive univalent interactions with H-donors. Compound II is the one-electron oxidized, intermediate form. Some H-donors, e.g. o-dianisidine, produce a direct, two-electron transfer reduction (Claiborne and Fridovich, 1979a). Nitrogenous compounds (nucleophilic catalysts pyridine, imidazole), may stimulate this transfer (Claiborne and Fridovich, 1979b). 

We have reported a number of cyclization reactions. The one- and two-N containing five and six-membered, saturated and unsaturated heterocycles were synthesized from C to Cs aliphatics like alcohols, aldehydes, ketones, in presence of ammonia and other amines [11-33]. For example, 3,5-lutidine was synthesized from propionaldehyde or propanol, formaldehyde and ammonia over modified ZSM-5 catalysts. The yield of 3,5-lutidine was in the range of 40 to 65 wt% at 60-90% conversion of propionaldehyde over modified ZSM-5 catalysts at 400 C. In the reaction of ethanol, formaldehyde and ammonia over ZSM-5 catalyst pyridine and picolines were obtained. The reaction route or mechanism is shown in Fig. 2 and 3. In the reaction of acetaldehyde, formaldehyde and ammonia over ZSM-5 pyridine and 3-Picoline were obtained. On the other hand, 2- and 4-Picolines were obtained in the reaction of acetaldehyde and ammonia. 

KEYWORDS Oxidation, NMO, CHP, cyclohexene, styrene, Ru(n)catalyst, pyridine and picoline... 

Catalyst Pyridine adsorption /mggcf Bronsted sites / % Lewis sites / %... 

Catalyst Pyridine conversion (%) B-py L-py Hj uptake of M/SiOj (ml/g metal)... 

Heterocyclic Compounds. Such materials undergo catalytic hydrogenation to yield the corresponding saturated derivatives. Thus, pyrrole is slowly converted to pyrrolidine at 200 C over either a nickel or copper-chromium oxide catalyst pyridine and pyridine derivatives behave similarly. Compounds such as furan and dihydropyran reduce rapidly and behave more like olefins in reactivity. Similarly, thiophene is converted to the tetrahydro derivative. 

Das et al. [8] described an operationally simple procedure for microwave-activated acetylation of carbohydrate alcohols by acetic anhydride, which uses only 0.1 equiv. of the powerful indium chloride catalyst. Peracetates were produced in good to excellent yields. Comparison of this method with others which use well established catalysts (pyridine, I2, Cu(OTf)2, C0CI2), either with an appropriate solvent or neat (following standard conditions), shows that under microwave irradiation conditions indium chloride is the best choice providing higher yields than those without microwave energy. 

Oxidative coupling polymerization in SCCO2 has been demonstrated for the synthesis of poly(2,6-dimethylphenylene oxide) 27. The polymerization of 2,6-dimethylphenol in the presence of oxygen is conducted using CuBr as the catalyst, pyridine and a block copolymer of styrene and 1,1-dihydroperfluorooctyl acrylate (PS- -PFOA) as a stabilizer in SCCO2 (350 bar) at 40 C. The polymerization occurred via a dispersion process and produced the polymer in a 74% yield with high molecular weight (17 000) (Scheme 46). 

Dioctyltin diisooctylthioglycollate catalyst, PU two-pack coatings Dibutyltin bis (laurylmercaptide) catalyst, PU elastomers Ferric acetylacetonate N-Hydroxyethy I pi perazi ne catalyst, purified terephthalic acid polyesters Manganese acetate (ous) catalyst, PVC suspension polymerization Lauroyl peroxide catalyst, pyridine synthesis Cobaltocene... 

The reaction of an acyl chloride with an alcohol to form an ester occurs rapidly and does not require an acid catalyst. Pyridine is often added to the reaction mixture to react with the HCI that forms. (Pyridine may also react with the acyl chloride to form an acylpyri-dinium ion, an intermediate that is even more reactive toward the nucleophile than the acyl chloride.)... 

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