Which anion is more acidic: TsO- or CN-?

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The discussion centers on the acidity comparison between TsOH (p-MeC6H4SO2H) and HCN, establishing that TsOH is significantly more acidic with a pKa of approximately -7, while HCN has a pKa around 9. This indicates that TsO- is a weaker base compared to CN-, which is a strong base. The conversation highlights the relationship between acidity and the leaving ability of anions in SN2 reactions, emphasizing that a stronger acid corresponds to a weaker conjugate base and better leaving group ability.

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Which is more acidic: TsOH or HCN? (Ts is p-MeC6H4SO2-).
 
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TsOH. TsOH has a pKa around -7, HCN is around 9.
 
You may think from the reverse side; if you have the basic equivalents of these acids, the basicities are reversed. Let me give an example, sodium salts of these acids are bases, but sodium cyanide is a very strong base whereas sodium tosylate is not that strong.
 
chem_tr said:
You may think from the reverse side; if you have the basic equivalents of these acids, the basicities are reversed. Let me give an example, sodium salts of these acids are bases, but sodium cyanide is a very strong base whereas sodium tosylate is not that strong.

:smile: Yeah I was working on this substitution reaction when this came along so I wanted to compare the leaving abilities of TsO- and CN- hence this problem. I did not know anything about their basic strengths. Instead we've been told to make acids from these anions (conjugate) and compare their acidic strengths. The stronger the acid, we weaker its conjugate base and correspondingly, the greater its leaving ability in a SN2 rxn.

Thanks and Cheers
Vivek
 

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