Why is sulfate a good leaving group

We have a few choices: 1 react the alcohol with p-toluenesulfonyl chloride abbreviated TsCl , which will convert the —OH group into a sulfonic acid ester, making it a much better leaving group--then react the ester with sodium bromide to produce 1-bromobutane; 2 react the alcohol with phosphorus tribromide PBr 3 , which converts the —OH into a "—P OH X 2 " leaving group where X is either —Br or —OH , and which also produces free bromide ions which react with the electrophile, replacing the new leaving group, all in one reaction mixture; or 3 using a strong acid to protonate the —OH group in the presence of the bromide ion, which changes the leaving group from hydroxide to water, and allows the bromide to react with it in the same mixture.

We will use the last of these methods. Safety: 1-butanol and 1-bromobutane are both flammable liquids and irritants-- no flames will be allowed, and wear gloves while handling them. Concentrated sulfuric acid is strongly corrosive and toxic--wear gloves while handling it, and be sure to wash your gloves and your hands immediately after handling it. Sodium bromide, sodium bisulfite and calcium chloride are all irritants--gloves are recommended.

The distillate contains both water and 1-bromobutane with a little sulfuric acid mixed in. Purify your product as follows:. Decant the clear, dried liquid into a or mL round bottom flask. Be careful not to let any of the solid sodium sulfate crystals get into the distillation pot. Discard any forerun but start collecting the sample that distills above o C.

In real reaction mechanisms, these groups are not good leaving groups at all. For example, fluoride is such a poor leaving group that S N 2 reactions of fluoroalkanes are rarely observed. If we move down the periodic table, size increases. With an increase in size, basicity decreases, and the ability of the leaving group to leave increases. The relationship among the following halogens, unlike the previous example, is true to what we will see in upcoming reaction mechanisms.

Resonance Increases the Ability of the Leaving Group to Leave: As we learned previously, resonance stabilized structures are weak bases.

Therefore, leaving groups that form resonance structures upon leaving are considered to be excellent leaving groups. Alkyl sulfates and sulfonates like the ones shown make excellent leaving groups. This is due to the formation of a resonance stabilized structure upon leaving. The Nature of the Leaving Group In order to understand the nature of the leaving group, it is important to first discuss factors that help determine whether a species will be a strong base or weak base.

Title: Carboxyl group participation in sulfate and sulfamate group transfer reactions. Full Record Other Related Research. Abstract The pH dependence for the hydrolysis of N- 2-carboxyphenyl sulfamic acid exhibits a plateau region corresponding to participation of the carboxyl function.

Chemical Labs. Hopkins, A, and Williams, A. Carboxyl group participation in sulfate and sulfamate group transfer reactions.