Condensations bases, pyridine

Commercial Manufacture of Specific Pyridine Bases. Condensation of paraldehyde with ammonia at 230°C and autogenous pressure (eq. 22) is used to manufacture 5-ethyl-2-methylpyridine (7). This is one of the few Hquid-phase processes used in the industry to make relatively simple aLkylpyridines, and one of the few processes known to make a single alkylpyridine product selectively. 

It seems reasonable that polyester cyclics could be prepared by an extension of the /wendo-high-dilution [17] chemistry used for the preparation of cyclic carbonate oligomers [18, 19] however, such proved not to be the case. Brunelle et al. showed that the reaction of terephthaloyl chloride (TPC) with diols such as 1,4-butanediol did not occur quickly enough to prevent concentration of acid chlorides from building up during condensation [14]. Even slow addition of equimolar amounts of TPC and butanediol to an amine base (triethylamine, pyridine or dimethylaminopyridine) under anhydrous conditions did not form cyclic oligomers. (The products were identified by comparison to authentic materials isolated from commercial PBT by the method of Wick and Zeitler [9].)... 

The choice of amines is important, however, in that they must be strongly basic. Unlike the usual condensations of phosgene and of dicar-boxylic acid chlorides, this system does not go at all well with weaker bases like pyridine, even when used in large excess. Pyridines and dial-kylanilines form highly colored side products and do not promote the rapid formation of high polymer (Table VI). 

Myriad polydentate aza-macrocycles have been reported 41. The extent of the subject forces limitation of this discussion to only macrocycles containing a pyridine or dipyridine subunit. Most of these coronands have been synthesized by a SchifF base condensation of an aldehyde or ketone with a hfc-primary amine in the presence of a metal ion. The metal ion acts as a template, resulting in dramatic increases in yield of the desired cyclic product over linear polymerization products42 46. Lindoy and Busch45 have described this effect in two ways, kinetic and thermodynamic. If the metal ion controls the steric course of a series of stepwise reactions, the template effect is considered to be kinetic. If the metal ion influences an equilibrium in an organic reaction sequence by coordination with one of the reactants, the template effect is termed thermodynamic. It is the kinetic effect that is believed to be operative in most metal ion-assisted (in situ) syntheses of... 

The only other example of a Schiff base condensation with dipyridine to form a macrocyclic complex has been reported by Tasker et al.112) in which 2,6-diformyl-pyridine or 2,6-diacetylpyridine is condensed with 6,6 -dihydrazmo-2,2 -dipyridine (132) in the presence of zinc(II) to afford a pentagonal bipyramidal complex 133. The rigidity of the system results in an equatorial Ns donor set that is essentially planar water molecules occupy the axial positions. 

As with the aza coronands previously discussed, the majority of the coronands containing oxygen and nitrogen have been synthesized by Schiff base condensation or via a nucleophilic substitution of a halide on a compound processing either pyridine or dipyridine subunits. 

In 1887, Pade described a piece of apparatus that enabled researchers to determine precisely the absolute densities of coffees and to detect coffee frauds involving manipulation of green coffees and watering of roast coffees. In this connection he mentions and comments on a fraudulent method whereby products released during roasting are condensed and reinserted into the coffee beans. After a summary analysis he deduces that this concentrated liquid contains caffeine, ammonia, amines, ammonia salts, acrid bases near pyridinic compounds and fatty acids. By watering down the still-hot coffee with this mixture, 14 to 15% of the lost weight can be fraudulently restored to it. 

Fig. 64. Two tetramers. Left, is the iMn,0,(tphpn)3 [ tetramer. Right, LMni (2-OH picpn)2] tphpn = N,N, A+ A+tetrakisfpyridylrnethyl)-1,3-diaminopropan-2-o]. 20Hpicpn is the Schiff-base condensation product of pyridine-2-carboxaldehyde with 1,3-diamino-propan-2-ol. [Reproduced with permission from (334) and (333), respectively. Copyright 1991 and 1996 the American Chemical Society, respectively.]...

The known compounds of this class are listed in table 6. The (2 + 2) Schiff-base condensation of hydrazine and 2,6-diacetylpyridine in the presence of the perchlorates of the smaller lanthanides, Tb(III)-Lu(III), has been reported to yield complexes of the 14-member, six-nitrogen macrocyclic ligand VI (Radecka-Paryzek 1981a), formulated as [M(H20)2(VI)](C104)-4H20. With the larger lanthanides, complexes of the three-quarter cycle diketone VII were instead isolated complexes of 2,6-diacetyl-pyridine were also occasionally obtained. 

A new thiophene-based monomer bearing a condensed pyridine group (84) was synthesized to obtain a low-gap polymer but the maximum absorption of the polymer was found at a high energy (560 nm, 2.2 eV) [336]. A real lowering of the gap was obtained from a condensed thiadiazole unit (85) with maximum polymer absorption at 934 nm (1.3 eV) [337]. Recently by further insertion of a pyrazine ring (86) the maximum absorption has been increased to 990 nm (1.25 eV) and the threshold of absorption lowered to 0.3 eV [338] so... 

The acid may also be prepared by the condensation of furfural with malonic acid in the presence of pyridine fiiiylmalonic acid is intermediately formed, which is decomposed upon heating In the presence of the base ... 

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. 

Primary amides condense with hydroxybenzaldehydes in a manner similar to amines. This reaction is often conducted in the presence of sodium acetate or an organic base such as pyridine. For example, the reaction of sahcylaldehyde and propionamide produces sahcyhdene propionamide (58). 

Historical. Pyridines were first isolated by destructive distillation of animal bones in the mid-nineteenth century (2). A more plentifiil source was found in coal tar, the condensate from coking ovens, which served the steel industry. Coal tar contains roughly 0.01% pyridine bases by weight. Although present in minute quantities, any basic organics can be easily extracted as an acid-soluble fraction in water and separated from the acid-insoluble tar. The acidic, aqueous phase can then be neutrali2ed with base to Hberate the pyridines, and distilled into separate compounds. Only a small percentage of worldwide production of pyridine bases can be accounted for by isolation from coal tar. Almost all pyridine bases are made by synthesis. 

Most processes in use in the 1990s make pyridines by condensation of ammonia with aldehydes or ketones either in the vapor phase or in the Hquid phase. These processes are based on the pioneering work of Chichibabin (3). Commercial practice of that process was not reali2ed until some 50 years after its discovery (74,75). 

The cyclic sulfur imides readily undergo condensation reactions in the presence of a base, e.g., pyridine. For example, the reaction of S7NH with sulfur halides, S Cla or SOCI2, produces the series (S7N)2Sx (x = 1, 2, 3, 5), or (S7N)2S0, respectively. The bicyclic compound S11N2 (6.6) is obtained by treatment of 1,3-S6(NH)2 with The reaction... 

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