Chlorides reactivity order

Pivalates. The selective pivaloylation of sucrose with pivaloyl (2,2-dimethylpropionyl) chloride has been thoroughly investigated (56). The reactivity of sucrose toward pivaloylation was shown to be significantly different from other sulfonic or carboxyflc acid chlorides. For example, reaction of sucrose with four molar equivalent of toluene-/)-sulfonyl chloride in pyridine revealed, based on product isolation, the reactivity order ofO-6 0-6 > 0-1 > 0-2 (57). In contrast, a reactivity order for the pivaloylation reaction, under similar reaction conditions, was observed to be 0-6 0-6 > 0-1 > 0-4. 

The second-order rate constants for the reaction of a number of amines with benzyl chloride are tabulated below. Calculate A// and A5 from the data. Offer an explanation for the relative reactivity order for the amines. What trends do you observe in A// with reactivity ... 

The reaction of substituted 1-arylethyl chlorides with K OC(CH3)3 in DMSO does not follow a Hammett correlation. Instead, the reactivity order is />-N02 > p-MeO > P-CF3 > P-CH3 > H > p-Cl. What explanation can you offer for the failure to observe a Hammett relationship ... 

As a consequence of these reactivity differences, it s usually possible to convert a more reactive acid derivative into a less reactive one. Acid chlorides, foi instance, can be directly converted into anhydrides, thioesters, esters, and amides, but amides can t be directly converted into esters, thioesters, anhydrides, or acid chlorides. Remembering the reactivity order is therefore a way tc keep track of a large number of reactions (Figure 21.2). Another consequence, a noted previously, is that only acyl phosphates, thioesters, esters, and amides are... 

The reaction of an alcohol with an acid chloride is strongly affected by steric hindrance. Bulky groups on either partner slow down the reaction considerably, resulting in a reactivity order among alcohols of primary > secondary > tertiary. As a result, it s often possible to esterify an unhindered alcohol selectively in the presence of a more hindered one. This can be important in complex syntheses... 

Phenanthridine (74) was converted by NBS into the 2-bromo derivative (40%) (55JA6379), but the bromine-sulfuric acid-silver sulfate reagent gave low yields of 1-, 4-, and 10-bromophenanthridines in the ratio (1 6.4 9.5), a reactivity order which contrasts with that found in nitration (1 > 10 > 4 > 2) (69AJC1105). Phosphoryl chloride converted phenanthridine 5-oxide into the 6-chloro derivative, but when that position was blocked by a phenyl substituent, the reductive chlorination process gave a 2-chloro compound (84MI2). 

Vitamin B12 catalyzed also the dechlorination of tetrachloroethene (PCE) to tri-chloroethene (TCE) and 1,2-dichloroethene (DCE) in the presence of dithiothreitol or Ti(III) citrate [137-141], but zero-valent metals have also been used as bulk electron donors [142, 143]. With vitamin B12, carbon mass recoveries were 81-84% for PCE reduction and 89% for TCE reduction cis-l,2-DCE, ethene, and ethyne were the main products [138, 139]. Using Ni(II) humic acid complexes, TCE reduction was more rapid, leading to ethane and ethene as the primary products [144, 145]. Angst, Schwarzenbach and colleagues [140, 141] have shown that the corrinoid-catalyzed dechlorinations of the DCE isomers and vinyl chloride (VC) to ethene and ethyne were pH-dependent, and showed the reactivity order 1,1-DCE>VC> trans-DCE>cis-DCE. Similar results have been obtained by Lesage and colleagues [146]. Dror and Schlautmann [147, 148] have demonstrated the importance of specific core metals and their solubility for the reactivity of a porphyrin complex. 

Aluminum trichloride and boron trifluoride as additives have a similar effect on the fluorination of (trichloromethyl)benzene by antimony(III) fluoride. With the additives, the reaction starts even at O C but no exchange is observed in the absence of the catalysts.12 The relative exchange reactivity order of the antimony halides is as follows antimony(III) fluoride < anti-mony(III) fluoride + antimony/V) chloride < antimony(V) dichlorotrifluoride, antimony/V) di-bromotrifluoride < antimony/V) fluoride.3... 

Electrophilic chlorination of quinoline under neutral conditions occurs in the orientation order 3 > 6 > 8. Hammett ct+ values predict an order for electrophilic substitution of 5 > 8 = 6 > 3. The reactivity order can be affected by substitution of an electron-withdrawing group in the benzene ring, which directs the chlorination to the pyridine ring. Thus, NCS in acetic acid or sulfuryl chloride in o-dichlorobenzene converts 8-nitroquinoline into 3-chloro-8-nitroquinoline in high yield (91M935). 

The diplatinum complexes [Pt(jU-H)SiR3(PCy3)]2 catalyze the addition of silanes R3SiH (R = Me, Et, PhCH2) Ph, OEt, Cl) to pentene-1, hexene-1, styrene, allyl chloride and 2-methylpropene. The relative reactivity order in silane is given, and the catalyst substrate ratio is 10-4-10-6 1. The majority of the reactions are carried out at ambient temperature and are exothermic. Dienes are also hydrosilylated.223 The complexes also catalyze the hydrosilylation of butyne-1, phenylacetylene, butyne-2 and diphenylacetylene in 70-90% yield. The... 

The reactivity order of the halides is I > Br > Cl F. Whereas magnesium and lithium react well with chlorides, bromides, and iodides, zinc is satisfactory... 

A notable feature in all these coupling protocols is that the coupling rates of iron-phosphorus systems, of the (salen)iron complex 5, the Fe(acac)3 catalyst, and catalyst 10 with respect to the alkyl halide are rather uncommonly bromide> iodide>chloride (entries 3, 4, 9, 13), whereas the reactivity order for iron-amine catalyst systems is iodide>bromide>chloride (entries 1, 5, 6). 

These conversions of acids into acid chlorides complete all the methods we need to convert acids into any acid derivatives. You can convert acids directly to esters and now to acid chlorides, the most reactive of acid derivatives, and can make any other derivative from them. The chart below adds reactions to the reactivity order we met earlier. 

All these acid derivatives can, of course, be hydrolysed to the acid itself with water alone or with various levels of acid or base catalysis depending on the reactivity of the derivative. To climb the reactivity order therefore, the simplest method is to hydrolyse to the acid and convert the acid into the acid chloride. You are now at the top of the reactivity order and can go down to whatever level you require. 

This principle may also be illustrated by some real cases. In the codimerization of propene and hexene it is important primarily to minimize the dimerization of the reactive propene. In order to favor the codimerization, a stage injection of propene according to the principle in Fig. 1 was therefore performed [2]. A similar process design with distributed additions of chlorine was applied in the chlorination of propene to allyl chloride in order to suppress different side reactions [3]. For liquid-phase processes, a distributed feed to the cascade of stirred reactors was a more natural variant. This was applied in the sulfuric acid alkylation of / obutane, where the olefin feed has to be subdivided due to selectivity reasons and the goal was to reach a desired octane number of the product [4]. 

The acid chloride reacts rapidly with water and the acid produced rapidly attacks another molecule of acid chloride. The anhydride reacts much more slowly (pfCjH of Cl is -7, of RCOJ is about +5) with water so there is a good chance of stopping the reaction there especially when we add a low concentration of water in acetone solution. This chance is made a certainty because the solid anhydride precipitates from solution and is no longer in equilibrium with the other compounds. It is usually possible to descend the reactivity order of acid derivatives (text, p. 287). 

---