Pyridine 4-tert-butylpyridine

Addition of a bulky pyridine base Some workers have added an equivalent of 2,6-di-tert-butylpyridine or 2,6-di-tert-butyl-4-methylpyridine to the glycosylation mixture. While the reasons for this addition have not been discussed, one can note that according to a speculative equation for the glycosylation reaction ... 

Indeed, where reactions at a ring carbon take place under relatively mild conditions, special circumstances are at work. For example, 2,6-tert-butylpyridine combines with sulfur trioxide in liquid sulfur dioxide at -10 C to give the corresponding 3-sulfonic acid (Scheme 2.3). An explanation is that the bulky tert-butyl groups prevent access of the large electrophile to N-1. Steric hindrance is much less at C-3 and sulfonation is diverted to this site using the free pyridine as the substrate. 

The Soft Nef-Reaction was possible using the sterically shielded 2,6-di-tert-butylpyridine (49). But when the concave pyridine 3c was used, different products (nitro compounds 45 or carbonyl compounds 47) were found for... 

The cores of the W6 clusters are very similar to those of the Mo6 analogues, and they are composed of the regular octahedra of six tungsten atoms capped by eight sulfur atoms (41, 43, 44). The W-W distances are almost the same, and difference in terminal ligands has little effect on the geometry (Table I). Only in the case of tert-butylpyridine complexes has a very small compression of the octahedron been observed in the c-axis direction (44). The bond order for the W—N bonds in the pyridine complexes is much weaker than that for the triethyl-phosphine analogue (43). 

Figure 6.5 (a) Structure of porphyrin clips 11, Znll and Mnll. (b) Two approaches in which Mnll is used as an epoxidation catalyst in combination with pyridine or 4-tert-butylpyridine as the axial ligand. 

Steric shielding of the heteroatom in pyridine results in non-nucleophilic bases such as 2,6-di-tert-butylpyridine and its 4-methyl congener (the latter is easily... 

The importance of chemical structure in determining ease of sulfonation is further illustrated in the pyridine series. These compounds as a group are very, difficult to sulfonate, ordinarily requiring a mercury catalyst at over 250°C using oleum. 2,6-Di-tert-butylpyridine has been found, on the other hand, to sulfonate easily even at — 10°C, using SO3 dissolved in SOj. In this exceptional case, steric hindrance prevents formation of the difficultly sulfonatable addition compound with SO3. 

Type and distribution of aluminium and iron in the framework of zeolite MCM-22 were investigated using adsorption of ds-acetonitrile, pyridine and 2,6-di-tert-butylpyridine followed by FTIR spectroscopy, sodium ion-exchange and UV-Vis spectroscopy of Co " ions located in cationic positions. Detailed analysis of aluminium and iron distribution among single ions, ion pairs, Bronsted and Lewis sites and internal and external surface is provided. 

Similarly, Karge et al. [398] employed pyridine and 2,6-di-tert-butylpyridine to differentiate between internal and external acid sites of zeolite crystallites. In this respect, another possibility is the use of lutidine [139] or quinoline. The latter probe was employed by Corma et al. [693] for the determination of external Bronsted and Lewis acid sites of H, Na-Y and Al, Na-Y zeolites (cf. also [694,695]). For a characterization of the external Bronsted and Lewis acidity of ZSM-5 samples, Keskinen et al. [696] utilized as sufficiently bulky bases trimethylsi-lyldiethylamine and, like Karge et al. [398], 2,6-di-ferf-butylpyridine. For the discrimination of external from internal acid sites of shape-selective H-ZSM-5 catalysts,Take et al. [135] utilized pyridine andabulkytrialkylamine (e.g.,Et3N, n-Pr3N and n-Bu3N) as a pair of probes, with the former indicating the total amount of acid sites. For quantitative evaluation they determined the extinction... 

Ethyl chloroformate added dropwise at 0° during 10 min. to a mixture of A-tert-butylpyridine and a soln. of er -butylmagnesium chloride in tetrahydrofuran, then treated at 0° with water -> l-ethoxycarbonyl-2,4-di-terr-butyl-l,2-dihydro-pyridine. Y 55%, - In the absence of ethyl chloroformate, pyridine derivs. react poorly with Grignard compds. F. e. s. G. Fraenkel, J. W. Cooper, and C. M. Fink, Ang. Ch. 82, 518 (1970). 

In a series of papers, Ford and co-workers described the photophysical and photochemical properties of these luminescent clusters in detail [46-58]. In addition to complexes 4a and 4b, time-resolved emission spectra of the tetranu-clear copper(I) iodide clusters [Qi4l4(L)4] with a series of substituted pyridines [L = 4-tert-butylpyridine (4c), 4-benzylpyridine (4d), pyridine-dj (4e), 4-phe-nylpyridine (4f), 3-chloropyridine (4g), piperidine (4h), P"Bu3 (4i)] have also been studied [49]. The photophysical data are summarized in Table 1. In general, in toluene solution at 294 K, the complexes revealed a low-energy emission at 678-698 nm and a weaker, higher energy emission at 473-537 nm. The emission spectrum of 4a in toluene at 294 K is shown in Fig. 2... 

Pyridine is indispensable in boronate polymerization the B-N interaetion between boronic aeid and pyridine allows boronate ester-ifieation to oecur more easily than under amine-free eonditions. 2,6-Di-tert-butylpyridine, which contained sterically hindered tert-butyl groups, which prevent the B-N interaction, had a negligible effeet on the solution. The Lewis dependence of pyridines in particle formation was investigated (Figure 12.3). Although no reaction occurred in the presenee of a weak base... 

Pyridine derivatives, such as 4-tert-butylpyridine (TBP), are frequently added to the electrolytes as additives to enhance the open-circuit photovolt-... 

Pyridine is an excellent solvent for LiAlHj reactions. In general, ketones can be reduced to alcohols under mild conditions. However, certain ketones under> go reductive cleavage, which may be inhibited by using the hindered 2-tert-butylpyridine in place of pyridine.—E ... 

Another type of steric effect is the result of an entropy effect. The compound 2,6-di-fert-butylpyridine is a weaker base than either pyridine or 2,6-dimethylpyridine. The reason is that the conjugate acid (8) is less stable than the conjugate acids of nonsterically hindered pyridines. In all cases, the conjugate acids are hydrogen bonded to a water molecule, but in the case of 8 the bulky tert-butyl groups restrict rotations in the water molecule, lowering the entropy. 

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