Catalyst, alumina pyridine

HYDROGENATION CATALYSTS Bis-(pyridine)dimethylformamidcdichlororbo-dium borohydride. Iron pentacarbonyl. Lindlar catalyst. Nickel boride. Palladium-on-calcium carbonate. Rhodium-on-alumina. Rhodium-on-carbon. Ruthenium trichloride hydrate. Triton dodecacar-bonyL Tris(tiiplienylpho ine)chloto-... 

Bipyridine has been prepared by the action of ferric chloride, iodine, or a nickel-alumina catalyst on pyridine at temperatures ranging from 300° to 400°. It has also been obtained from the reaction of 2-bromopyridine and copper. The present procedure is a modification of a previously published, general method. The W7-J nickel catalyst was developed from the description of the W7 Raney nickel catalyst of Billica and Adkins. ... 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Tetrahydrofurfuryl alcohol reacts with ammonia to give a variety of nitrogen containing compounds depending on the conditions employed. Over a barium hydroxide-promoted skeletal nickel—aluminum catalyst, 2-tetrahydrofurfur5iarnine [4795-29-3] is produced (113—115). With paHadium on alumina catalyst in the vapor phase (250—300°C), pyridine [110-86-1] is the principal product (116—117) pyridine also is formed using Zn and Cr based catalysts (118,119). At low pressure and 200°C over a reduced nickel catalyst, piperidine is obtained in good yield (120,121). 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Reaction of formaldehyde, methanol, acetaldehyde, and ammonia over a siUca alumina catalyst at 500°C gives pyridine [110-86-1] and 3-picoline... 

The alkylation of pyridine [110-86-1] takes place through nucleophiUc or homolytic substitution because the TT-electron-deficient pyridine nucleus does not allow electrophiUc substitution, eg, Friedel-Crafts alkylation. NucleophiUc substitution, which occurs with alkah or alkaline metal compounds, and free-radical processes are not attractive for commercial appHcations. Commercially, catalytic alkylation processes via homolytic substitution of pyridine rings are important. The catalysts effective for this reaction include boron phosphate, alumina, siHca—alurnina, and Raney nickel (122). 

The formation of trace amounts of 2,2 -bipyridine following reaction between pyridine and ammonia in the presence of a variety of catalysts led Wibaut and Willink to develop a method for the preparation of 2,2 -bipyridine from pyridine under the influence of a nickel-alumina catalyst. Using a pyridine-to-catalyst ratio of 10 1, temperatures between 320° and 325°C, and pressures between 42 and 44 atm, 2,2 -bipyridine was formed in yields of 0.30-0.67 gm per gram of catalyst. This method w as later applied to -picoline, to quino-line, - and to some of its derivatives, ... 

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

Reaction of -picoline with a nickel-alumina catalyst has been reported to give a mixture of four isomeric dimethylbipyridines, one of which has been identified at 6,6 -dimethyl-2,2 -bipyridine. With palladium-on-carbon, 2,4-lutidine was found to be more reactive than pyridine,and the isolated biaryl has been assigned the structure (2). However, some confusion arises from the statement that this... 

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Adsorbed CO and NO were used as probes to Investigate the effects of Co concentration and sulfide on the nature and numbers of exposed metal sites on reduced catalysts containing 1 to 6 wt% Co and 8 wt%. Mo on three alumina supports. Exposure of Mo Ions decreased with Increased Co concentration. Exposure of Co Ions typically reached a maximum at 2-4% Co. Sulfide decreased exposure of all metal Ion sites and Increased exposure of reduced metals. Effects of preadsorbed pyridine and 2,6-lutldlne, known poisons, on the exposure of metal sites, plus other evidence. 

Gopalan, U., Hydrodenitrogenation of Pyridine over Alumina Supported Platinum Catalyst. Master of Applied Science Thesis. University of Otawa, Chemical Engineering. 1998, p. 69. 

When the dehydration of menthol is carried out on an acidic alumina or at a long contact time the 2-menthene can isomerize to the more stable 1- and 3-menthenes. In order to avoid the consecutive reactions which proceed by acid catalysis, the alumina can be modified either by adding pyridine to the menthol or by passing ammonia over the catalyst during dehydration. 

Pure alumina catalyst prepared either by hydrolysis of aluminum isopropoxide or by precipitation of aluminum nitrate with ammonia, and calcined at 600-800°, contains intrinsic acidic and basic sites, which participate in the dehydration of alcohols. The acidic sites are not of equal strength and the relatively strong sites can be neutralized by incorporating as little as 0.1 % by weight of sodium or potassium ions or by passing ammonia or organic bases, such as pyridine or piperidine, over the alumina. 

Sato et al. [195] have studied the surface borate structures and the acidic properties of alumina-boria (3-20 wt.%) catalysts prepared by impregnation method using B(MAS)-NMR measurements and TPD of pyridine, as well as their catalytic properties for 1-butene isomerization. The number of Brpnsted acid sites was found to increase with increasing boria content, and the catalytic activity was explained by the strong Brpnsted acid sites generated by BO4 species on the surface of alumina. 

A number of routes are available for the synthesis of 2,2 -bipyridines where one of the pyridine rings is built up from simpler entities. For example, condensation of 2-(aminomethyl)pyridine (31) with acetaldehyde or acetylene over a silicon-alumina catalyst at 450°C gives 2,2 -bipyridine, ° whereas 2-cyanopyridine reacts with acetylene at 120°C in the presence of a cobalt catalyst to afford 2,2 -bipyridine in 95% yield.2-Acetylpyridine with acrolein and ammonia gives 2,2 -bipyridine in the presence of dehydrating and dehydrogenating catalysts, and related condensations afford substituted 2,2 -bipyridines. ° In a similar vein, condensation of benzaldehyde with 2 mol of 2-acetylpyridine in the presence of ammonia at 250°C affords 2,6-di(2-pyridyl)-4-phenylpyridine, ° and related syntheses of substituted 2,2 6, 2"-terpyridines have been described. Likewise, formaldehyde with two moles of ethyl picolinoylacetate and ammonia, followed by oxidation of the product and hydrolysis and decarboxylation, affords a good... 

As in the synthesis of other bipyridines, several routes to 4,4 -bipyridine have been devised where one of the pyridine rings is built up from simpler components. For example, a dimer of acrolein reacts with ammonia and methanol in the presence of boron phosphate catalyst at 350°C to give a mixture of products including 4,4 -bipyridine (3.4% yield), and in a reaction akin to ones referred to with other bipyridines, 4-vinylpyridine reacts with substituted oxazoles in the presence of acid to give substituted 4,4 -bipyridines. ° ° Condensation of isonicotinaldehyde with acetaldehyde and ammonia at high temperatures in the presence of a catalyst also affords some 4,4 -bipyridine, and related processes give similar results,whereas pyran derivatives can be converted to 4,4 -bipyridine (56% conversion), for example, by reaction with ammonia and air at 350°C with a nickel-alumina catalyst. Likewise, 2,6-diphenyl-4-(4-pyridyl)pyrylium salts afford 2,6-... 

In contrast to laboratory scale operations, four-bond formation processes are of considerable importance as industrial routes to pyridine derivatives and have been investigated in Considerable detail. Vapour phase condensation of aldehydes and ketones with ammonia and amines in the presence of a variety of silica/alumina catalysts containing different promoters (e.g. cobalt(II) chloride) can give excellent yields of substituted pyridines (e.g. equation 151), and the nature of the products formed can be largely controlled by change in the stoichiometry of the reactants and variation of experimental conditions (equation 152). 

Mixtures of pyridines are obtained when allynic alcohols (268) and ammonia are passed over catalysts such as cadmium oxide on alumina at 360-400 °C (59IZV1629). 

There are a very large number of patented processes for the synthesis of pyridines, often in very small yields, from ketones and ammonia. Most of the syntheses must involve the condensation of two molecules of the carbonyl compound to give an a,/3 -unsaturated aldehyde or ketone, and such unsaturated compounds can be used directly. The early work on the vapour-phase catalytic processes dates from the 1920s and a series of papers by Chichibabin. In one of these (24JPR(107)154) he records the use of acrolein, acetaldehyde, and ammonia over an alumina catalyst at 370-380 °C to give a poor yield of pyridine and a very poor yield of 3-methylpyridine. The major problems are to separate the mixtures of products from the considerable amount of tarry material. Many catalysts and many mixtures of ketones have since been used a few of the better yields are reported here. 

Very little is known about the behaviour of different catalysts only a few comparisons of alumina and silica—alumina have been made. On Al2-03—Si02, the disproportionation of diethylamine is more rapid by one order of magnitude than its deamination on A1203, the rates are comparable [149], The activity of alumina for aniline disproportionation is higher than of silica—alumina [150]. The steric demands of the alumina surface are higher than those of silica—alumina as the comparison of the chemisorption of pyridine and 2,6-dimethylpyridine has shown [158]. 

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