What is the name of the CO2Na group? [closed]








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I'm trying to identify the name of every functional group sticking off the sides of tartrazine (FD&C Yellow No. 5), and the one I can't find anywhere is this $\ce{COONa}$ group. Does anyone know how to describe it? Is it really two groups put together?




This is simply the [salt](https://en.wikipedia.org/wiki/Carboxylate) of a carboxylic acid and sodium hydroxide, with the general reaction looking something like this:


![](https://i.stack.imgur.com/Qq2jm.png)


The names of carboxylate salts can be derived from that of the original carboxylic acid and the base used, "-oic acid" becoming "[metal] -oate" (e.g. benz**oic acid** reacting with sodium hydroxide to become **sodium** benz**oate**). If part of a more complex molecule, the $\ce{COO-}$ group is treated like any other substituent and given the name "carboxylate".


This can be seen in the name of tartrazine: 
trisodium [...]-3-**carboxylate**, as well as the name of the sodium salt of citric acid:
trisodium 2-hydroxypropane-1,2,3-tri**carboxylate**.


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