Is there any acid which releases a gas when neutralized with hydroxide?

Out of curiosity, is there any acid which releases a gas upon neutralization with sodium hydroxide? Most acids that I know of release hydrogen upon reaction with metals, but not upon reaction with alkalis like sodium hydroxide.




The simplest and most obvious answer is the ammonium ion, closely followed by the phosphonium ion $\ce{PH4+}$. Both are acids as defined by the Arrhenius theory and by the Brønsted-Lowry theory; however, they always require a counterion. Upon proton displacement, they form gaseous compounds — $\ce{NH3}$ and $\ce{PH3}$, respectively — which will diffuse out of solution given enough time.


The solubility of ammonia in water is much higher than that of carbon dioxide, though; so it takes longer for ammonia to be released and no visible bubbling occurs. Yet, the gas evolution can be shown by sticking a moist indicator paper above the solution; fumes of ammonia will colour it whichever colour means *basic* on that paper.


$$\begin{align}\ce{NH4+ + OH- &-> NH3 (g) ^ + H2O}\tag{1}\\[1.2em]
\ce{PH4+ + H2O &-> PH3 (g) ^ + H3O+}\tag{2}\end{align}$$


A less obvious answer and maybe a bit of a stretch is the monochloride of oxalic acid, $\ce{ClCOCOOH}$. This compound is not stable; however, its basic structural motif is formed in many organic mechanisms, e.g. in the Swern oxidation as a $\ce{DMS}$ adduct ($\ce{Cl-CO-COO-S^+Me2}$). Once a chloride ion attacks sulfur nucleophilicly and thereby displaces what formally would be the monoanion of oxalic acid monochloride, this breaks down into carbon dioxide, carbon monoxide and chloride.


$$\ce{Cl- + Me2S^+-OCO-CO-Cl -> ClS^+Me2 + CO2 ^ + CO ^ + Cl-}\tag{3}$$


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