Acidity of lactic acid and propanoic acid

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Discussion Overview

The discussion revolves around the acidity comparison between lactic acid and propanoic acid, as well as the reaction of ketones with phosphorus pentachloride (PCl5). The scope includes theoretical aspects of acidity and organic chemistry reactions.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that lactic acid is a stronger acid than propanoic acid due to the electronegativity of the oxygen atom in the hydroxyl group, which may increase the polarity of the -OH bond in the carboxyl group, facilitating the release of H+.
  • Another participant agrees with the assessment that lactic acid is stronger, attributing this to the electron-withdrawing effect of the -OH group in the alkyl chain.
  • Regarding the reaction of ketones with PCl5, one participant states that ketones react to form acid chlorides, while another later corrects this by stating that the product is not called an acid chloride but rather alkyl chlorides, specifically geminal.

Areas of Agreement / Disagreement

There is some agreement on the acidity of lactic acid being stronger than that of propanoic acid, but the exact nature of the products formed from the reaction of ketones with PCl5 remains contested.

Contextual Notes

Participants have not fully resolved the terminology regarding the products of ketone reactions with PCl5, and there may be assumptions about the definitions of acidity and reaction products that are not explicitly stated.

Michael_Light
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Homework Statement



i) Is lactic acid,CH3CH(OH)COOH a stronger or weaker acid than propanoic acid (CH3CH2COOH)

ii) Another question is does ketone reacts with phosphorus pentachloride PCl5?

Homework Equations





The Attempt at a Solution



(i) I guess lactic acid is a stronger acid because the oxygen atom on the hydroxyl group is very electronegative thus increases the polarity of the -OH bond on the carboxyl group, so H+ are more easily released. (Please correct me if i am wrong)

(ii) I can't find any relevant information from my textbook and even on google, but I encountered this type of question from my exercise book.. Can anyone guide me?
 
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Hi Michael!

For (i) you are correct that lactic acid is stronger. -OH in an alkyl chain acts as electron withdrawing due to -I effect.

For (ii) you probably didn't google it well, as it is quite a standard reaction in organic chemistry. :-p

Ketones react with phosphorus penta-chloride to give acid chlorides.

http://www.ch.ic.ac.uk/local/organic/tutorial/DB_Carbonylnotes1.pdf
 
Infinitum said:
...snip

Ketones react with phosphorus penta-chloride to give acid chlorides.

Close, but not quite. The product isn't called an acid chloride.
 
chemisttree said:
Close, but not quite. The product isn't called an acid chloride.

Whoops, I meant alkyl chlorides, specifically geminal.
 

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