Tert-Butyl chloride alcohol

When tert-butyl chloride with sodium hydroxide in a mixture of water and acetone, the rate of formation of tert-butyl alcohol is dependent on the concentration of tert- butyl chloride, but is independent of the concentration of hydroxide ion. 

More recent patents describe the following preparation from a-methylcinnam-aldehyde. a-Methylcinnamaldehyde (from benzaldehyde and propionaldehyde) is hydrogenated to a-methyldihydrocinnamic alcohol. The alcohol is alkylated with tert-butyl chloride or isobutene to 4-tert-butyl-o -methyldihydrocinnamic alcohol, which is subsequently dehydrogenated to the desired aldehyde [152, 153]. 

Many secondary and tertiary halides undergo El elimination in competition with the SN1 reaction in neutral or acidic solutions. For example, when tert-butyl chloride solvolyzes in 80% aqueous ethanol at 25°, it gives 83% tert-butyl alcohol by substitution and 17% 2-methylpropene by elimination ... 

Treatment of tert-butyl alcohol with concentrated HC1 gives tert-butyl chloride. 

FIGURE 4.7 The mechanism of formation of tert-butyl chloride from tert-butyl alcohol and hydrogen chloride. 

We first applied the solvatochromic equation (SCE) to solvolysis of tert-butyl chloride (t-BuCl) to determine if the method could give a reasonable result for this much-studied reaction (7). Abraham et al. (11) had previously attempted correlation of these rates with the SCE without the cavity term, but as Bentley and Carter (12) have noted, an unsatisfactory result was achieved (7). First, TFE and hexafluoroisopropyl alcohol (HFIP) did not fit the correlation. Second, no rate dependence on solvent nucleophilicity 0 was found, despite other works indicating a weak dependence on this parameter (12, 13). Also, different correlations were observed for hydroxylic and nonhydroxylic solvents Bentley considered this finding to indicate that the dehydrohalogenation transition state (in nonhydroxylic solvents) and the solvolysis transition state (in hydroxylic solvents) were significantly different and thus concluded that the two types of reactions should not be included in the same correlation. 

When Hughes (Section 6.6) and co-workers studied the reaction of terT-butyl chloride with water they found the kinetics leading to formation of tert- mxy alcohol to be quite different than for other substitution reactions that they had studied. 

Cyclopentyl cyanide from cyclopentanol NCCH2CH2CN from ethyl alcohol Isobutyl iodide from isobutyl chloride Isobutyl iodide from tert-butyl chloride... 

Tert.Butyl chloride ( CcHjCl ) + Ethyl alcohol... 

Let us now consider another mechanism for nucleophilic substitution the SnI reaction. When tert-butyl chloride reacts with sodium hydroxide in a mixture of water and acetone, the kinetic results are quite different than for the reaction of chloromethane with hydroxide. The rate of formation of tert-butyl alcohol is dependent on the concentration of tert-butyl chloride, but it is independent of the concentration of hydroxide ion. Doubling the tert-butyl chloride concentration doubles the rate of the substitution reaction, but changing the hydroxide ion concentta-tion (within limits) has no appreciable effect tert-Butyl chloride reacts by substitution at virtually the same rate in pure water (where the hydroxide ion is 10 M) as it does in 0.05M aqueous sodium hydroxide (where the hydroxide ion concentration is 500,000 times larger). (We shall see in Section 6.10 that the important nucleophile in this reaction is a molecule of water.)... 

The interest of chemists in this topic originated in two findings reported more than a century ago that exposed the influence of solvents on the rate of esterification of acetic acid by ethanol, estabhshed in 1862 by Berthelot and Saint-Gilles, and on the rate of qua-temization of tertiary amines by alkyl halides, discovered in 1890 by Menschutkin. In his study, Menschutkin found that even so-called inert solvents had strong effects on the reaction rate and that the rate increased by a factor about 700 from hexane to acetophenone. Subsequent kinetic studies have revealed even higher sensitivity of the reaction rate to the solvent. Thus, the solvolysis rate of tert-butyl chloride increases 340,000 times from pure ethanol to a 50 50 v/v mixture of this alcohol and water," and by a factor of 2.88x10 " from pentane to water. Also, the decaiboxylation rate of 6-nitrobenzisoxazol 3-carboxylate increases by a factor of 9.5x10 from water to HMPT. ... 

Apparatus and procedure Closely similar to the preparation of tert.-Ci,H3MgCl, cyclohexyl-MgCl and cyclopentyl-MgCl (see Exp. 2). The yield (estimated from the results obtained from reactions with this reagent) is at least 90%. Here, too, it is essential to use M-butyl chloride which is free from butyl alcohol. 

Consider the reaction of tert butyl alcohol with hydrogen chloride... 

The molecularity of an elementary step is given by the number of species that undergo a chemical change m that step Transfer of a proton from hydrogen chloride to tert butyl alcohol is bimolecular because two molecules [HCl and (CH3)3COH] undergo chemical change... 

With the potential energies shown on a common scale we see that the transition state for formation of (CH3)3C is the highest energy point on the diagram A reaction can proceed no faster than its slowest step which is referred to as the rate determining step In the reaction of tert butyl alcohol with hydrogen chloride formation of the... 

FIGURE 4 12 Potential energy diagram for the reaction of tert butyl alcohol and hydrogen chloride according to the SnI mechanism... 

The first step of this new mechanism is exactly the same as that seen earlier for the reaction of tert butyl alcohol with hydrogen chloride—formation of an alkyloxonmm ion by proton transfer from the hydrogen halide to the alcohol Like the earlier exam pie this IS a rapid reversible Brpnsted acid-base reaction... 

The major difference between the two mechanisms is the second step The second step m the reaction of tert butyl alcohol with hydrogen chloride is the ummolecular dis sociation of tert butyloxonium ion to tert butyl cation and water Heptyloxonium ion however instead of dissociating to an unstable primary carbocation reacts differently It IS attacked by bromide ion which acts as a nucleophile We can represent the transition state for this step as... 

These common features suggest that carbocations are key intermediates m alcohol dehydra tions just as they are m the reaction of alcohols with hydrogen halides Figure 5 6 portrays a three step mechanism for the acid catalyzed dehydration of tert butyl alcohol Steps 1 and 2 describe the generation of tert butyl cation by a process similar to that which led to its for matron as an intermediate m the reaction of tert butyl alcohol with hydrogen chloride... 

Like the reaction of tert butyl alcohol with hydrogen chloride step 2 m which tert butyloxonium ion dissociates to (CH3)3C and water is rate determining Because the rate determining step is ummolecular the overall dehydration process is referred to as a ummolecular elimination and given the symbol El... 

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