Pyridine improving

Athene epoxidation.1 In the presence of a Mn-porphinate, particularly 5.10,15,20-tetra-2,6-dichlorophenylporphinatomanganese(III) acetate,2 MMPP can spoxidize alkenes in the presence of a phase-transfer catalyst in high yield. Addition of a base (pyridine) improves the rate. 

Ceo solubility in thiophenol is more than 2 times greater than that in toluene as opposed to pyridine. Improved C6o solubility in thiophenol is attributable to the increase in the overall a-electron density of the benzene core. When acted upon by a positive mesomeric effect of a SH-group, a-electron density is localized mainly in the ortho- and /rt/ra-positions, i.e. in the reaction centers for interaction between thiophenol molecules and C6o. 

The authors explained these results on the basis of an intramolecular complexation of the metal ion by the enolate, giving a conformation where the pyridinyl ring is gauche, rather than anti, to the benzoyl group. Thus, -elimination from the chelated enolate would generate the thermodynamically less stable cfs-alkene, which rapidly undergoes Michael addition with a second equivalent of the enolate. The addition of pyridine improved the... 

The electrospun webs produced with pyridine were also examined under SEM. Two observations could be made. Firstly, the addition of pyridine improved the quality of PCL fibers, by effectively suppressing beads and forming finer-sized uniform fibers. Secondly, for optimum results, the lower the PCL concentration used, the higher was the amount of pyridine needed to achieve the bead-free nano-size fibers (e.g. 10% PCL solution required in excess of 1 % pyridine, whereas 17.5% solution required less than 0.2% pyridine). 

Rapid addition of a pre-formed carbamate anion solution (generated from dialkyl amine, N-cyclohexyl-N, N, N",N"-tetramethylguanidine (1 equiv.), and pyridine (1 equiv.) under a pressure of carbon dioxide) to a solution of thionyl chloride (1 equiv.) at —10 °C led to an exothermic reaction. Rapid aqueous extraction (to remove salts and SO2 ) of the crude reaction mixture and distillation of the residue gave good isolated yields of the carbamoyl chloride (40-80%). The results obtained using various reagents in this reaction are shown in the table below. It is not yet clear as to why added pyridine improves the yield of carbamoyl chloride (from 72 to 85%). It is possible that pyridine acts as a trap for the sulfur dioxide that is likely to be formed during the course of the reaction. 

Terpolymers of butadiene, styrene and vinyl pyridine (75/15/15) have been of some interest in rubber-to-textile bonding, the presence of the vinyl pyridine improving the degree of adhesion as compared with straight SBR latices. 

Silver(I) salts can also function as an terminal oxidant in the C2-selective olefination of pyridine improvements in both yield and C2 selectivity were observed when less basic AgOAc was employed in place of Ag2C03 as an oxidant. Maximal yields were achievable when pivalic acid was added. Of note, only small amounts of C3 product were detected. 

The above procedure may also be carried out in the presence of 1 ml. of dry pyridine with some alcohols improved yields may be obtained by this modification. 

Bromination of fatty acids in the a-position can be effected quite readily in the presence of phosphorus trichloride, red phosphorus or pyridine as catalysts or halogen carriers with acetic acid, the addition of acetic anhydride (to ensure the absence of water) improves the yield and facilitates the bromination. Examples are —... 

The conversion of a carbonyl compound by ammonium polysulphide solution into an amide with the same number of carbon atoms is known as the Willgerodt reaction. The procedure has been improved by the addition of about 40 per cent, of dioxan or of pyridine to increase the mutual solubility of the ketone and aqueous ammonium polysulphide the requisite temperature is lowered to about and the yield is generally better. 

Dow Chemical Company purchased the rights to MacaHum s patents (14), initiated a detailed study of the process and other improved syntheses of PPS in the 1950s and early 1960s, and pubUshed the results of their investigation (9,15,16). Clearly, alternative routes to PPS were desirable and the most promising of these involved the nucleophilic self-condensation of cuprous -bromothiophenoxide, carried out at 200—250°C in the soHd state or in the presence of pyridine (16) ... 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

The first synthesis of sorbic acid was from crotonaldehyde [4170-30-3] and malonic acid [141-82-2] in pyridine in 32% yield (2,17,18)- The yield can be improved with the use of malonic acid salts (19). One of the first commercial methods involved the reaction of ketene and crotonaldehyde in the presence of boron trifluoride in ether at 0°C (20,21). A P-lactone (4) forms and then reacts with acid, giving a 70% yield. 

In practice, these cleavage reactions are difficult to control, and usually mixtures of products form, even with stoichiometric quantities of reagents. Selectivity improves at lower temperatures, higher dilutions, and in the presence of polar solvents, eg, pyridine. This method is not used to prepare the lower alkylated—arylated organotins outside the laboratory. 

Nitrogen nucleophiles used to diplace the 3 -acetoxy group include substituted pyridines, quinolines, pyrimidines, triazoles, pyrazoles, azide, and even aniline and methylaniline if the pH is controlled at 7.5. Sulfur nucleophiles include aLkylthiols, thiosulfate, thio and dithio acids, carbamates and carbonates, thioureas, thioamides, and most importandy, from a biological viewpoint, heterocycHc thiols. The yields of the displacement reactions vary widely. Two general approaches for improving 3 -acetoxy displacement have been reported. One approach involves initial, or in situ conversion of the acetoxy moiety to a more facile leaving group. The other approach utilizes Lewis or Brmnsted acid activation (87). 

Liquid-phase chlorination of butadiene in hydroxyhc or other polar solvents can be quite compHcated in kinetics and lead to extensive formation of by-products that involve the solvent. In nonpolar solvents the reaction can be either free radical or polar in nature (20). The free-radical process results in excessive losses to tetrachlorobutanes if near-stoichiometric ratios of reactants ate used or polymer if excess of butadiene is used. The "ionic" reaction, if a small amount of air is used to inhibit free radicals, can be quite slow in a highly purified system but is accelerated by small traces of practically any polar impurity. Pyridine, dipolar aptotic solvents, and oil-soluble ammonium chlorides have been used to improve the reaction (21). As a commercial process, the use of a solvent requites that the products must be separated from solvent as well as from each other and the excess butadiene which is used, but high yields of the desired products can be obtained without formation of polymer at higher butadiene to chlorine ratio. 

The Perkin reaction is of importance for the iadustrial production of coumarin and a number of modifications have been studied to improve it, such as addition of a trace of iodine (46) addition of oxides or salts of metals such as iron, nickel, manganese, or cobalt (47) addition of catalytic amounts of pyridine (48) or piperidine (49) replacement of sodium acetate by potassium carbonate (50,51) or by cesium acetate (52) and use of alkaU metal biacetate... 

The raw material has to be washed to remove impurities. Diluted sodium hydroxide allows the removal of phenols and benzonitrile, and diluted sulphuric acid reacts with pyridine bases. The resulting material is distilled to concentrate the unsaturated compounds (raw feedstock for coumarone-indene resin production), and separate and recover interesting non-polymerizable compounds (naphthalene, benzene, toluene, xylenes). Once the unsaturated compounds are distilled, they are treated with small amounts of sulphuric acid to improve their colour activated carbons or clays can be also used. The resulting material is subjected to polymerization. It is important to avoid long storage time of the feedstock because oxidation processes can easily occur, affecting the polymerization reaction and the colour of the coumarone-indene resins. 

In the absence of an added solvent, 3-alkyIpyridines, 4-alkyl-pyridines, and 3,4-dialkylpyridines all gave yields of substituted 2,2 -bipyridines that were up to three times greater than that of 2,2 -bipyridine from pyridine under similar conditions. With 3-ethyl-4-methylpyridine a marked improvement in yield was ob.served when the reaction was carried out at about 150°C in a vacuum, rather than at the atmospheric boiling point (195°C) of this base. This effect has also been observed with some other bases but the amount of 3,3, 5,5 -tetramethy 1-2,2 -bipyridine from 3,5-lutidine could not be increased in this way, and this pyridine was as unreactive as the 2-substituted pyridines. This finding is undoubtedly related to the reluctance of 3-substituted pyridines to form 3,3 -disubstituted 2,2 -bipyridines. 

N— compounds used as acid inhibitors include heterocyclic bases, such as pyridine, quinoline and various amines. Carassiti describes the inhibitive action of decylamine and quinoline, as well as phenylthiourea and dibenzyl-sulphoxides for the protection of stainless steels in hydrochloric acid pickling. Hudson e/a/. refer to coal tar base fractions for inhibition in sulphuric and hydrochloric acid solutions. Good results are reported with 0-25 vol. Vo of distilled quinoline bases with addition of 0 05m sodium chloride in 4n sulphuric acid at 93°C. The sodium chloride is acting synergistically, e.g. 0-05m NaCl raises the percentage inhibition given by 0-1% quinoline in 2n H2SO4 from 43 to 79%. Similarly, potassium iodide improves the action of phenylthiourea . 

The interest in asymmetric synthesis that began at the end of the 1970s did not ignore the dihydroxylation reaction. The stoichiometric osmylation had always been more reliable than the catalytic version, and it was clear that this should be the appropriate starting point. Criegee had shown that amines, pyridine in particular, accelerated the rate of the stoichiometric dihydroxylation, so it was understandable that the first attempt at nonenzymatic asymmetric dihydroxylation was to utilize a chiral, enantiomerically pure pyridine and determine if this induced asymmetry in the diol. This principle was verified by Sharpless (Scheme 7).20 The pyridine 25, derived from menthol, induced ee s of 3-18% in the dihydroxylation of /rcms-stilbene (23). Nonetheless, the ee s were too low and clearly had to be improved. 

The Karl Fischer procedure has now been simplified and the accuracy improved by modification to a coulometric method (Chapter 14). In this procedure the sample under test is added to a pyridine-methanol solution containing sulphur dioxide and a soluble iodide. Upon electrolysis, iodine is liberated at the anode and reactions (a) and (b) then follow the end point is detected by a pair of electrodes which function as a biamperometric detection system and indicate the presence of free iodine. Since one mole of iodine reacts with one mole of water it follows that 1 mg of water is equivalent to 10.71 coulombs. 

PcH2 was obtained for the first time in 1907 as a byproduct during the preparation of 2-cyanobenzamide.50 However, this discovery initiated no interest at that time. In 1927, PcCu was prepared in 23% yield by heating 1,2-dibromobenzene with copper(I) cyanide in pyridine.51 The term phthalocyanine was first used by Linstead in 1933.52 From 1929 to 1939, Linstead et al. elucidated the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines.52 - 61... 

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