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Two key ingredients found in many soaps are PEG 150 distearate and ethylhexyl glycerin. Both can be synthesized from glyceryl tristearate (Figure 1) .
Figure 1 Formation of PEG 150 distearate and ethylhexyl glycerin from glyceryl tristearateThe first step in this process requires the saponification of glyceryl tristearate. The resulting stearate molecules can then react with PEG 150 in an acid-catalyzed Fischer esterification to form PEG 150 distearate. The glycerol produced during saponification is used as a nucleophile to form ethylhexyl glycerin through a base-catalyzed S_N2 reaction with an ethylhexyl halide.Studies have shown that hand washing with soap can substantially reduce the number of germs present on hands and that washing hands before preparing food is particularly effective in reducing illness. Researchers examined the effect of washing for 20 seconds with different amounts of soap containing PEG 150 distearate and ethylhexyl glycerin and found an inverse correlation between the volume of soap used and the amount of bacteria recovered from the hands. The data are shown in Figure 2.
Figure 2 Bacteria recovered from hands after washing with varying amounts of soapThe researchers then investigated the effect of hand washing with different kinds of soap on the transfer of bacteria from hands to objects. Volunteers washed with a fixed volume of soap for 30 seconds, then handled sterilized plastic spheres for 30 seconds. Bacteria were then recovered from the spheres. The results are shown in Table 1.Table 1 Bacteria Recovered from Objects
Adapted from Fuls JL, Rodgers ND, Fischler GE, et al. Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Appl Environ Microbiol. 2008.
-Researchers produced ethylhexyl glycerin using a partially deuterated ethylhexyl halide and generated the product shown below. What was the configuration of the deuterated carbon prior to the reaction?

Question

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Two key ingredients found in many soaps are PEG 150 distearate and ethylhexyl glycerin. Both can be synthesized from glyceryl tristearate (Figure 1) .

Figure 1 Formation of PEG 150 distearate and ethylhexyl glycerin from glyceryl tristearateThe first step in this process requires the saponification of glyceryl tristearate. The resulting stearate molecules can then react with PEG 150 in an acid-catalyzed Fischer esterification to form PEG 150 distearate. The glycerol produced during saponification is used as a nucleophile to form ethylhexyl glycerin through a base-catalyzed S_N2 reaction with an ethylhexyl halide.Studies have shown that hand washing with soap can substantially reduce the number of germs present on hands and that washing hands before preparing food is particularly effective in reducing illness. Researchers examined the effect of washing for 20 seconds with different amounts of soap containing PEG 150 distearate and ethylhexyl glycerin and found an inverse correlation between the volume of soap used and the amount of bacteria recovered from the hands. The data are shown in Figure 2.

Figure 2 Bacteria recovered from hands after washing with varying amounts of soapThe researchers then investigated the effect of hand washing with different kinds of soap on the transfer of bacteria from hands to objects. Volunteers washed with a fixed volume of soap for 30 seconds, then handled sterilized plastic spheres for 30 seconds. Bacteria were then recovered from the spheres. The results are shown in Table 1.Table 1 Bacteria Recovered from Objects

Adapted from Fuls JL, Rodgers ND, Fischler GE, et al. Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Appl Environ Microbiol. 2008.
-Researchers produced ethylhexyl glycerin using a partially deuterated ethylhexyl halide and generated the product shown below.

What was the configuration of the deuterated carbon prior to the reaction?

Quizplus · Accepted Answer

11ecba2d_1265_83ac_a3bf_252a7b4ae180_MD0008_00 If the electrophile in an S_N2 reaction is a chiral center, its stereochemistry will always be inverted by the reaction. An electrophile in the S configuration prior to the reaction will adopt an R configuration after the reaction, and vice versa. To determine whether a configuration is R or S, prioritize each atom attached to the chiral center in order of atomic weight. If the chiral center is bonded to two or more identical atoms, continue to the next atom in each chain and repeat until a difference is found. After making assignments, position the lowest priority group at the back of the molecule and determine whether the other groups are arranged in clockwise or counterclockwise order. Clockwise corresponds to an R configuration, and counterclockwise corresponds to an S configuration. The deuterated carbon shown in ethylhexyl glycerin is a chiral center that acted as the electrophile in an S_N2 reaction. Therefore, its configuration must have been inverted during the reaction. Based on the above rules, the deuterated ethylhexyl glycerin shown is in the R configuration. Therefore, the deuterated ethylhexyl halide used in the reaction must have been in the S configuration. (Choices B and D) The product is in the R configuration, so the reactant must have been in the S configuration because electrophiles that are chiral centers undergo inversion of configuration in S_N2 reactions. (Choice C) The ethylhexyl halide was in the S configuration, but this configuration was not preserved by the S_N2 reaction. Educational objective: S_N2 reactions result in the inversion of configuration of the electrophile if the electrophile is a chiral center. An electrophile in the S configuration will adopt the R configuration after the reaction, and vice versa.

Passage Two Key Ingredients Found in Many Soaps Are PEG 150