" Could you provide the formula for this
please."

Butyric acid is H3C-CH2-CH2-CO2H.  This can be shown as RCO2H to make is simpler to see.

Butryic anhydride is H3C-CH2-CH2-CO-O-OC-CH2-CH2-CH3.  This can be shown as RCO-O-OCR for the same reason.

When you split that RCO-O-OCR linkage in the anhydride by adding water on the left side you get RCO2H and on the right side you get HO2CR.  R simply stands for all that CHn stuff in the full formula.

If this is still not clear please ask again and I will try and do better.

The anhydride is much more reactive than the butyric acid.  Butyric acid is going to be metabolized by much the same routes your body uses to metabolize any linear organic acid such as acetic acid in vinegar or the long chain fatty acids that all to many of us have in excess on our bellies.  It can be viewed as a normal food product in reasonable amounts.  The anhydride on the other hand will react with your tissues, particularly in your lungs, resulting in some cell death and what amounts to a chemical burn.  And, a heck of a lot of lung irritation to boot resulting in a pretty nasty cough for a while.  Like most chemicals with either of these chemicals the harm done is mainly a matter of how much you are exposed to.  Traces are not a big deal.  Large exposures could be life threatening.  The biggest immediate threat is likely edema in your lungs, particularly if you have even mild COPD.  Essentially a chemical induced pneumonia.  Any respirator rated for organic vapors and acid gasses should provide adequate protection.  I would have no concern handling multi pound quantities of either in the lab using normal lab hoods and handling precautions.  But bear in mind I have run reactions with a half pound or more of sodium cyanide and am used to handling toxic materials.

Dick

" Any discovery made by the human mind can be explained in its essentials to the curious learner."  Professor Benjamin Schumacher talking about teaching quantum mechanics to non scientists.   "For every complex problem there is a solution which is simple, neat and wrong."  H. L. Mencken

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