2-chloro-2-methylpropane, solvolysis

Thomson O1" Click Organic Process to view animations showing the S 1 reaction of 2-methyl-2-propanol with HCI and the SN1 solvolysis of 2-chloro-2-methylpropane. 

They took as their standard reaction the SN1 solvolysis of the tertiary halide, 2-chloro-2-methylpropane (46), and selected as their standard solvent 80% aqueous ethanol (80% EtOH/20% H20) ... 

Another example of the effects of ultrasound on a solvolysis reaction can be found in the homogeneous hydrolysis of 2-chloro-2-methylpropane in aqueous alcoholic media (Eq. 3.3). This system has been the subject of numerous kinetic studies since it is one of the classic examples of a unrmolecular nucleophilic displacement reaction (termed... 

This maximum is thought, from viscosity and enthalpy of mixing studies (Fig. 5.42), to be due to the formation of a H-bonded monomer-water complex. Previous investigations of the solvolysis of 2-chloro-2-methylpropane had led us to conclude that low intensity ultrasound (< 2 W cm ) was capable of destroying H-bonds and if this were... 

Standard halide, 2-chloro-2-methylpropane (46). Here k. and fco are the rate constants for solvolysis of any halide, in solvent A and in the standard solvent, respectively. Ya has already been defined as a solvent parameter representing the ionising power of solvent A, while m is a compound parameter characteristic of the particular halide it is given the value 1-00 for the standard halide, 2-chloro-2-methylpropane (46). The actual value of m can be taken as a measure of the susceptibility of the solvolysis of a particular halide towards the ionising power, Ya, of that solvent ... 

The rate of solvolysis or de-hydrochlorination of /-butyl chloride (2-chloro-2-methylpropane) has been studied very extensively under standardized conditions, and the rate constant has been used as a characterization of solvent polarity. The reaction proceeds according to the scheme ... 

The solvolysis of 2-chloro-2-methylpropane is 335000 times faster in water than in the less polar solvent ethanol [40] cf. reaction type (a) in Table 5-4. 

Comparison of the solvolysis rate constants of 2-chloro-2-methylpropane obtained in water and in benzene solution reveals a rate acceleration of ca. 10 with increasing solvent polarity [47] f The solvolysis rate of 1-bromoadamantane in... 

In the SnI solvolysis reaction of 2-chloro-2-methylpropane, leading mainly to t-butanol and t-butyl ethers together with some f-butene, the term solvolysis is normally restricted to the reaction in water and other HBD solvents. In non-HBD solvents, however, the only reaction product is f-butene. For convenience, the term solvolysis is often used in the literature to cover both types of reaction, solvolysis and dehydrohalogenation of 2-chloro-2-methylpropane, because the solvent-dependent rate-determining step of both reactions, S l and El, is the same. For a detailed review on the heterolysis of tertiary haloalkanes in the gas phase and in solution, see G. F. Dvorko, E. A. Ponomareva, and N. 1. Kulik, Usp. Khim. 53, 948 (1984) Russ. Chem. Rev. 53, 547 (1984). 

Table 5-13. Rate constants and activation parameters for the SnI solvolysis of 2-chloro-2-methylpropane in six solvents at 25 °C [40],...

Fig. 5-13. Correlation between Ig A i [40] and the Kirkwood function (cr — l)/(2 r + 1) for the solvolysis of 2-chloro-2-methylpropane in binary 1,4-dioxane/water (A), ethanol/water (B), acetone/water (C), and methanol/water (D) mixtures at 25 °C cf. Eq. (5-13) in Section 5.3.1.

Reaction type 3 in Table 5-25 is best represented by the SnI solvolysis of 2-chloro-2-methylpropane cf. Eq. (5-13) in Section 5.3.1. Considering the heterolysis of the C—Cl bond, one would expect the activation volume to be positive because of the C—Cl stretching during the activation process. However, a negative activation volume of AF = —22.2 cm mol has been found for this solvolysis at 30 °C in ethanol/ water (80 20 cL/L), indicating a strong volume contraction due to solvation of the dipolar activated complex (electrostriction) [756]. Typical activation volumes for halo-alkane solvolyses in pro tic solvents are in the range of —15... —30 cm mol ... 

Since reaction rates can be strongly affected by solvent polarity cf. Chapter 5), the introduction of solvent scales using suitable solvent-sensitive chemical reactions was obvious [33, 34]. One of the most ambitious attempts to correlate reaction rates with empirical parameters of solvent polarity has been that of Winstein and his co-workers [35-37]. They found that the SnI solvolysis of 2-chloro-2-methylpropane (t-butyl chloride, t-BuCl) is strongly accelerated by polar, especially protic solvents cf. Eq. (5-13) in Section 5.3.1. Grunwald and Winstein [35] defined a solvent ionizing power parameter Y using Eq. (7-13),... 

Multiple regression analysis of Ig ki of the strongly solvent-dependent solvolysis/ dehydrohalogenation of 2-chloro-2-methylpropane (t-BuCl) for n = 21 solvents using the KAT equation (7-54) leads to Eq. (7-55b), with r = 0.997, and s = 0.242 [288] ... 

The composition of the reaction mixture formed in an Sjyjl reaction affects neither the rate of the reaction nor the value of the rate constant because the products all arise from a common intermediate, namely a carbocation, that is formed in the rate-determining step (Eq. 14.2). Thus, the four products that are likely to be formed in the solvolysis of 2-chloro-2-methylpropane in aqueous 2-propanol may individually be formed at different rates because of the differing values of the rate constants, and of the concentrations of the reagents that react with the... 

It is also clear that intramolecular strain (sometimes called back strain or B-strain ), which results from steric repulsion between groups attached to the carbon bearing the leaving substituent, also plays an important role in accelerating the reaction of haloalkenes. Such ground-state destabilization is, for example, used to account for the observations that, under the same conditions, 2-chloro-2,4,4-trimethylpentane undergoes solvolysis about 20 times faster than 2-chloro-2-methylpropane and 4-chloro-2,2,4,6,6-pentamethylheptane is nearly 500 times faster (Table 7.3) ... 

Solvolysis studies of alkyl halides in mixed solvents are common (see, e.g., Buncel and Millington, 1965). Grunwald and Winstein (1948) introduced the parameter Y, a measure of ionizing power based on the rate of solvolysis of 2-chloro-2-methylpropane (t-butyl chloride). It is a measure of the ability of the solvent to stabilize the ions that are generated in the unimolecular, ratedetermining first step ... 

An example of solvolysis important in physical organic chemistry is the solvolysis of t-butyl chloride (2-chloro-2-methylpropane), the rate of which is the basis of the Grunwald and Winstein (1948) parameter F, described in Section 2.10. 

The solvolysis of 2-chloro-2-methylpropane in water occurs by the mechanism... 

Experiment 3.1. Experimental determination of the rate constant and reaction order for the solvolysis of 2-chloro-2-methylpropane in ethanol-water mixture [2-4]... 

Figure 3.2 Dependence of the initial rate of solvolysis of 2-chloro-2-methylpropane with initial concentration of the solute in ethanol-water mixture. The slope of the hnear plot gives the rate constant k = 1.4 X lO sec at 20 °C.

We return to the solvolysis of 2-chloro-2-methylpropane in water discussed in Chapter 3 (Section 3.1). The rate-determining step of this reaction is the ionisation of the haloalkane, such that the reaction follows first-order kinetics. Thus, we can write... 

The confirmation of the reaction order is obtained by noting that for a first-order process the rate is directly proportional to the concentration. This dependence can be shown nsing the initial velocity for varions well-defined concentrations. The initial rate for each concentration is obtained from the tangent at time f = 0 of the experimental concentration-time cnrve. For the solvolysis of 2-chloro-2-methylpropane in water, the initial velocities obtained for different concentrations show a linear dependence on the initial concentration that passes through the origin, with a slope k, confirming that the reaction is first order (see Figure 3.2). 

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