Reaction times range

Most interest focuses on very fast reactions. This includes systems whose mean reaction times range from roughly 1 minute to 10 14 second. Reactions that involve bond making or breaking are not likely to occur in less than 10 13 second, since this is the scale of molecular vibrations. Some unimolecular electron transfer events may, however, occur more rapidly. 

The long reaction times (ranging from hours to days) frequently required for full conversions have, however, limited the exploitation of homogeneous catalysis in... 

In the case of 3-substituted cyclopentanones or cycloheptanones, derivatization with diamine is slower, and the reaction time ranges from a few minutes to several hours. This method is not applicable to acyclic ketones and enones. 

The reaction time ranges from 1.5 to about 4 hours. Progress of the reaction should be followed by determining the peroxide content of the oxidation mixture at half-hour intervals after all the hydrogen peroxide has been added. Approximately all the peroxide should be consumed before distillation is attempted. 

Efficient mixing. High surface-volume ratio Optimized heating transfer precise temperature control Side-reaction suppression Only soluble substrates-reagents are compatible. Limited reaction-time range small scale... 

However, the use of CH3SO3H as catalyst at room temperature resulted in the formation of monotransalkylated and ditransalkylated products [Eq. (21)]. The reaction was slow, with reaction times ranging from 2 to 3 days. The reaction could be made specific for either product by adjusting the acid concentration. Higher concentrations favored the formation of the ditransalkylated product. 

The use of catalytic amounts of [LiCo(B9C2Hn)2] (102) had several practical advantages (Sch. 60 and 61) (i) The conjugate addition of Si-1 to 12 proceeds equally fast (5 min) in Et20, dichloroethane, or CH2CI2 in the presence of 10 mol % 102. (ii) In contrast to the above mentioned dependence on the concentration of the LPDE system, in this reaction any of the substrates Si-1, Si-3, or Si-6 can be used under identical conditions using 10 mol % 102, except that reaction times range from 5 min to 1 h. (iii) When sterically encumbered substrates such as 122 are used, the combined use of equimolar amount of HMPA and 102 (10 mol % each) dramatically enhances 1,4-selectivity [112]. 

Leaving groups other than halogens have been used on the C-C fragment. For example, the use of a-tosyloxy ketones offers an alternative to the lachrymatory a-haloketones. The MW-mediated reaction of several para-substituted a-tosyloxy acetophenones with ra-substituted thiobenzamides was accomplished in 88-96% yields with reaction times ranging from 2 to 4 min <1998J(P1)4093>. Cyclization has also been reported without a leaving... 

In flash chemistry, extremely fast reactions are conducted in a highly controlled manner, and desired products are formed very quickly. Reaction times range from milliseconds to seconds. To accomplish such extremely fast reactions, we often need to activate molecules to make substrates with built-in high-energy content or prepare highly reactive reagents that react very quickly with substrates. There are several methods for activation, including thermal, photochemical, electrochemical, and chemical methods. In this chapter, we briefly survey these methods. 

Polymerization by Transition-Metal Complex Catalysts. Mlly M12, and M13 have been polymerized by Et3Al/TiCl4 catalysts between 50° and 80 °C in n-hexane, the reaction times ranging from a few hours to several days. The polymers obtained have the same structure as those obtained by cationic polymerization. By analogy with mechanisms proposed in the literature (38, 39), the structure shown in Equation 24 may be proposed for the active center. 

Sulfonation of Hydroxylamine Disulfonate. Seel et al. (14) studied the reaction between HADS and bisulfite and found that this reaction produced about 70% aminetrisulfonate (ATS) and 30% aminedisulfonate (ADS) in the temperature range from 25 to 60°C and ionic strength from 1.0 to 1.2 M, with reaction times ranging up to 4.5 hr at a pH of 7. The reaction proceeds according to Eqs. (14) and (15) ... 

Still another powerful method for the regeneration of carbonyl compounds from dialkylhydrazones is copper-catalyzed hydrolysis. The reagents that have been tested for this purpose are 2% aqueous cop-per(II) acetate solution at pH 4, copper(II) chloride in 0.05M phosphate buffer and 75% tetrahydrofu-ran/water, and copper(II) sulfate pentahydrate . Under the conditions of the hydrolysis, no reaction is observed in the absence of the copper(II) ion. Typical yields are 85-100%. Other functional groups like a-dicarbonyl, a-tricarbonyl, acetal and aldehydic formyl groups were not affected by this hydrolysis procedure. Nitrile formation in the case of aldehyde dimethylhydrazones was not a significant side reaction. However, reaction times ranged from 1 to 15 h. The reaction is believed to be nonoxidative in nature rather, the copper is believed to activate the C=N bond and catalyze hydrolysis. The dimethylhydrazine produced during hydrolysis also complexes irreversibly with the copper(II) ion to drive the reaction to completion. 

The rearrangement of these S-crotylic dithioacetals proceeds more slowly than that of the 5-allylic analogs. Several months at room temperature are required for completion of the rearrangement. If the rearrangement is run at 80 °C in cyclohexane solution, the reaction times range from 2.5 to 28 hours (Table 27). 

Sufficient reaction time was allowed in each test to insure complete reaction between the particular modifier and sulfur. With modifier concentrations in the range of 1-19 wt %, the reaction times ranged from less than 10 min at 220°C to over 120 min at 120 °C. Combinations of two modifiers, namely, dipentene—dicyclopentadiene and dipentene-sty-rene, were also tested. 

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