Deactivation, indirect

These pyridazines are subject to direct deactivation of the leaving group. It would appear from the conditions used in its reactions with ammonia (115°) and methylamine (50°) that 4-chloro-2-ethylthiopyrimidine (225) is somewhat deactivated (indirect). In various aminations of pyrimidines, the effect of an alkylthio group seems to be very mildly deactivating, like that of methyl groups. However, these surmises from the conditions used are not as reliable as the direct qualitative comparison described above and the kinetic data. 

Molecular fluorescence and, to a lesser extent, phosphorescence have been used for the direct or indirect quantitative analysis of analytes in a variety of matrices. A direct quantitative analysis is feasible when the analyte s quantum yield for fluorescence or phosphorescence is favorable. When the analyte is not fluorescent or phosphorescent or when the quantum yield for fluorescence or phosphorescence is unfavorable, an indirect analysis may be feasible. One approach to an indirect analysis is to react the analyte with a reagent, forming a product with fluorescent properties. Another approach is to measure a decrease in fluorescence when the analyte is added to a solution containing a fluorescent molecule. A decrease in fluorescence is observed when the reaction between the analyte and the fluorescent species enhances radiationless deactivation, or produces a nonfluorescent product. The application of fluorescence and phosphorescence to inorganic and organic analytes is considered in this section. 

Comparison of the ortho and para indirect deactivation in 155 and 156 with that in 151 and 152 would reveal the relative effectiveness of the two effects and the influence of the ring-position. Additional examples of deactivation are ortho indirect in 2-chloro-6-methoxy-pyrazine ortho direct in 4-chloro-5-methoxypyrimidine para direct in 2-chloro-5-methoxypyrimidine ortho and para indirect in the... 

The ortho indirect deactivating effect of the two methyl groups in 2,6-dimethyl-4-nitropyridine 1-oxide (163) necessitates a much higher temperature (about 195°, 24 hr) for nucleophilic displacement of the nitro group by chloride (12iV HCl) or bromide ions N HBr) than is required for the same reaction with 4-nitropyridine 1-oxide (110°). With 5-, 6-, or 8-methyl-4-chloroquinolines, Badey observed 2-7-fold decreases in the rate of piperidino-dechlorination relative to that of the des-methyl parent (cf. Tables VII and XI, pp. 276 and 338, respectively). 

The para direct deactivation (toward excess piperidine, 45°) by a 4-methyl substituent on 2-nitrobromobenzene (164) is greater than para indirect deactivation by a 5-methyl group (rate of displacement equivalent to absence of a methyl group). A similar result was obtained with 2-nitrochlorobenzenes substituted by methyl or methoxy groups in the reaction with piperidine in benzene. 

Amination of the deactivated carbanion of 4-benzylpyridine formed with excess sodamide presumably proceeds because the strong indirect deactivation is overcome by electrophilic attack by Na+ at the partially anionic azine-nitrogen and by concerted nucleophilic attack by H2N at the 2-position via a 6-membered cyclic transition state (75). However, in simple nucleophilic displacement a carbanion will be more deactivating than the corresponding alkyl group, as is true in general for anionic substituents and their non-ionic counterparts. 

The indirect deactivation in 2-amino-4-chloroquinoline (187) requires vigorous conditions (potassium hydroxide in hot ethylene glycol, or boiling propanolic propoxide for 16 hr) to displace the chloro group, which is stable to aqueous alkali and to hydriodic acid. The direct deactivation in 5-amino-2-chloro-3-cyano-6-methyl-pyridine (188) prevents reaction with alkoxide ion under conditions which produce smooth reaction of the des-amino analog. 

Direct deactivation by a methoxy group makes 3-chloro-6-methoxy-pyridazine unreactive toward sulfanilamide anion in contrast to its 6-chloro, 6-methyl, and 6-hydrogen analogs. Both direct and indirect deactivation of the two chlorines in 3,6-dichloro-4-methoxy-pyridazine (160) are possible the greater reactivity at the... 

Indirect deactivation by an alkoxy group is apparent in the sluggish reaction of 4-butoxy-2-chloroquinoline with w-butylamine (EtOH, 5 hr, 180°, but not at 80°). The chloro group in 2-chloro-4-ethoxy-quinoline is more reactive than that in the 4-chloro-2-ethoxy isomer toward alkoxides or amines in spite of the usually more effective para indirect deactivation in the former. For kinetic data on quinolines see Tables X and XI, pp. 336 and 338, respectively. 

An indirect hydrogenation process that is still under development is catalytic gasification. In this process, a catalyst accelerates the gasification reactions, resulting in the formation of hydrogen and CO, at relatively low temperatures. This process also promotes catalytic formation of methane at the same low temperature within the same reactor. Catalyst deactivation and costs have been a major impediment to the commercialization of this process. 

In a pressure study involving a multimeric enzyme, it will in general not be possible to decide how much of the effect is due to direct influence of pressure on the catalytic process and how much of it is due to indirect influence through subunit dissociation and accompanying deactivation. Generally, a self-association reaction may be expressed in either of two equivalent forms ... 

Protons, generated indirectly by deprotonation of an intermediate during anodic oxidation of an organic substrate, are obviously produced in stoichiometric amounts. Reactions induced by these protons are typically acid-catalyzed conversions of the initial oxidation product or proton-induced reactions/deactivation of unconverted substrate. 

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