Increased reactivity

The reactivity of mercerized cotton is increased by about 1 / times at lower temperature in comparison to that of unmercerized cotton. The increased reactivity is not so marked when mercerization is carried out under tension. The reactivity ratio is generally referred to as the ratio of copper number of the mercerized to unmercerized samples. The increased reactivity increases dye absorption, moisture sorption and chemical reaction, but at the same time it also accelerates the reaction with acids and oxidising agents and is susceptible to degradation. 

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The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

Reaction of various reagents (CH3I. CjHjI, PhCHO) on the organolithium products obtained by reaction of butyl-lithium with 2-methyl-4-phenylthiazole gives approximately 90% 5-substitution. The increased reactivity of the hydrogen in the 5-position can be explained by the fact that the -r J effect of a 4-methyl group would increase the electron... 

Increasing reactivity of alcohols toward hydrogen halides... 

Increasing reactivity of hydrogen halides m addition to alkenes... 

This pattern of increased reactivity resulting from carbonyl group prolonalion has been seen before m nucleophilic additions to aldehydes and ketones (Section 17 6) and... 

Sonochemistry can be roughly divided into categories based on the nature of the cavitation event homogeneous sonochemistry of hquids, heterogeneous sonochemistry of hquid—hquid or hquid—sohd systems, and sonocatalysis (which overlaps the first two) (12—15). In some cases, ultrasonic irradiation can increase reactivity by nearly a million-fold (16). Because cavitation can only occur in hquids, chemical reactions are not generaUy seen in the ultrasonic irradiation of sohds or sohd-gas systems. 

In view of the overall increased reactivity of furan compared with thiophene it would be anticipated that furan would be less regioselective in its reactions with electrophiles than thiophene. Possible reasons for the high regioselectivity of furan in electrophilic substitution reactions include complex formation between substrates and reagents and the ability of heteroatoms to assist in the stabilization of cationic intermediates (80CHE1195). 

Pyrazoles and imidazoles exist partly as anions (e.g. 108 and 109) in neutral and basic solution. Under these conditions they react with electrophilic reagents almost as readily as phenol, undergoing diazo coupling, nitrosation and Mannich reactions (note the increased reactivity of pyrrole anions over the neutral pyrrole species). 

One of the major differences between penicillins and cephalosporins is the possibility for a concerted elimination of the C-3 substituent in the case of cephalosporins (6->7). There is now considerable evidence to support the idea that an increase in the ability of the C-3 substituent to act as a leaving group results in an increased reactivity of the 8-lactam carbonyl (75JMC408). Thus, both the hydrolysis rate of the 8-lactam and antibacterial activity... 

NaH, THF, BnBr, Bu4N I, 20°, 3 h, 100%. This method was used to protect a hindered hydroxyl group. Increased reactivity is achieved by the in situ generation of benzyl iodide. ... 

All RBMK reactors have positive void coefficients which means that increasing the boiling rate increases the steam fraction in the core which increases reactivity causing more steam void which causes more reactivity and so on. Competing factors provide stability, but startup, shutdown and maneuvering below about 600 MWt are unstable, hence, there is a rule prohibiting extended operation below 700 Mwt. 

The use of acid chlorides instead of acid anhydrides has also been described. Wittig and coworkers converted propiophenone 31 to chromone 32 in 50% yield with chloroacetyl chloride in the presence of sodium chloroacetate at 190 C. Despite the acid chloride s increased reactivity, a high temperature was still required. 

There are conflicting generalizations in the heterocyclic literature as to the relative reactivity of a- and y-positions in azines toward nucleophiles. Variations in the relative reactivity are attributed in this and subsequent sections to specific factors operating in addition to activation by azine-nitrogen. Another possible source of variation may be a decrease in selectivity with increasing reactivity of one or both reagents, an effect established in electrophilic aromatic... 

Acid catalysis increases reactivity both para and ortho to the site of protonation. Coulombic attraction of an anionic nucleophile to the vicinity of the positive center will to some extent remove the proton (65), forming the less reactive azine and the nucleophile s... 

Increased reactivity toward amines and hydroxide ion is observed upon quaternization, e.g., 1-methyl-4,7-dichloroquinolinium ion. The effect of the positive charge in favoring substitution (cold alkali) at the adjacent 2-position is so great that about 20% of the 2-hydroicy-lation product (415) was isolated in addition to 35% of the compound (416) formed by displacement of the highly reactive 4-chloro group. 

Betlz has subsequently developed aniido [195] and phosphido [195, 196] mixed cuprate reagents featuring increased reactivity and greater thernial stability A use-... 

Studies of the influence of irradiation on the kinetics of oxidation have been confined to post-irradiation work. In general, prior irradiation increases reactivity, although there are considerable inconsistencies in the enhancements obtained The effects can be derived from an increased surface area associated with the swelling voids produced in the metal by the irradiation, and can also probably arise to a lesser extent from chemical effects of the fission products. 

The pKa s of five p-substituted benzoic acids (YC6H4C02H) follow. Rank the corresponding substituted benzenes (YC Hs) in order of their increasing reactivity toward electrophilic aromatic substitution, if benzoic acid has pK , = 4.19, which of the substituents are activators and which are deactivators ... 

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