[yash]

Ok so i am a beginner in organic chemistry and i came across comparing acidity.
Now according to various books i referred,anthranilic acid/ortho-amino benzoic acid is less acidic than benzoic acid.There was not sufficient explanation and therefore,my doubt.
According to my book,in o-hydroxy benzoic acid,the conjugate base is stabilized by hydrogen bonding between OH and COO negative ion,thus making the compound more acidic.
When i apply the same logic to this argument,apparently it fails.I want to know why.
Note-I am aware about nh2 being an exception to the ortho effect.But Then by same logic,shouldnt OH be an exception too?

[Babcock_Hall]

I don't know the answer to your question, but I thought that listing the values for ortho, meta, and para-substituted H₂N-benzoic acid, is a good place to start.  I used Williams pK_a table:
H2N- 4.98 4.79 4.92

[yash]

and the value of pka of benzoic acid is near 4.2 at room temp while that of ortho hydroxy benzoic acid is 2.97.
Update-I consulted another book and it says that OH substituted benzoic acid is strong because of intra molecular H bonding between OH and COO negative ion.
But again the question arises the same can be argued for NH2 and COO negative ion.
Appreciate your reply anyways,my teacher was also clueless.

[Babcock_Hall]

One way to assess the importance of a hydrogen bond is to look at a case in which there is one (oxygen) or two (nitrogen) alkyl groups.  The pK_a of ortho-methoxybenzoic acid is 4.09, and the meta- and para-isomers are 4.09 and 4.47, respectively.  The pK_a values for the three isomers of CH₃NH-substituted benzoic acid are 5.3 5.10 5.04
The three pK_a values of the isomers of (CH₃)₂N-benzoic acid are 8.42 5.10 5.03.  See what you make of these values.

[yash]

the pka values you mentioned are predictable.
Methoxy group isnt able to hydrogen bond with COOH(according to my reference book) and therefore it increases acidity by steric replusion only.In para position methoxy group's +Resonance effect is more powerful then -I effect therefore decreasing acidity .
In (CH3)2N-benzoic acid i am guessing Nitrogen is able to hydrogen bond in para posi(I am not sure) as i can account for no other reason that reduces its acidity so much.
Again It comes down to Why NH3 reduced acidity instead of increasing it same way as OH does :/