Editing Propionic acid (section)

==Properties==
Propionic acid has physical properties intermediate between those of the smaller carboxylic acids, [[formic acid|formic]] and [[Acetic acid|acetic]] acids, and the larger [[fatty acid]]s.  It is miscible with water, but can be removed from water by adding salt.  As with acetic and formic acids, it consists of [[hydrogen bond]]ed pairs of molecules in both the liquid and the vapor.

Propionic acid displays the general properties of carboxylic acids: it can form [[amide]], [[ester]], [[acid anhydride|anhydride]], and [[acyl chloride|chloride]] derivatives.  It undergoes the [[Hell–Volhard–Zelinsky halogenation|Hell–Volhard–Zelinsky reaction]] that involves α-[[halogenation]] of a carboxylic acid with [[bromine]], [[catalyst|catalysed]] by [[phosphorus tribromide]], in this case to form [[2-bromopropanoic acid]], {{chem|CH|3|CHBrCOOH}}.<ref>{{OrgSynth | first1 = C. S. | last1 = Marvel | first2 = V. | last2 = du Vigneaud | title = α-Bromoisovaleric acid | volume = 11 | pages = 20 | collvol = 2 | collvolpages = 93 | year = 1931 | prep = cv2p0093 | doi = 10.15227/orgsyn.011.0020 }}</ref>  This product has been used to prepare a [[racemic mixture]] of [[alanine]] by [[Solvolysis#ammonolysis|ammonolysis]].<ref>{{cite journal|title = Synthesis of ''d'',''l''-Alanine in Improved Yield from α-Bromopropionic Acid and Aqueous Ammonia|first1 = Walter C.|last1 = Tobie|first2 = Gilbert B.|last2 = Ayres|journal = [[Journal of the American Chemical Society]]|year = 1937|volume = 59|issue = 5|page = 950|doi = 10.1021/ja01284a510|doi-access = free| bibcode=1937JAChS..59..950T }}</ref><ref>{{OrgSynth | first1 = Walter C. | last1 = Tobie | first2 = Gilbert B. | last2 = Ayres | title = ''dl''-Alanine | prep = cv1p0021 | year = 1941 | collvol = 1 | collvolpages = 21 | doi = 10.15227/orgsyn.009.0004 |doi-access = free}}</ref>
<!--- Note: This Org Synth manuscript is in two parts; the Kendall and McKenzie part was first published in 1929 (vol 9, p. 4) and deals with a Strecker synthesis of alanine.  The second part by Tobie and Ayres was first published in JACS in 1937 and appended to the Kendall and McKenzie Org Synth report in collvol 1 in 1941.  It is the second part that relates to preparing alanine from 2-bromopropanoic acid.  Please be careful if checking / changing these reference, which do share most citation details.  --->

::[[File:Preparation of alanine from propionic acid.png|500px|class=skin-invert-image]]