Solution to spectroscopy challenge 12

Abstract

Malic acid was first isolated by Carl Wilhelm Scheele from apple juice in 1785. Scheele was born in 1742 in Stralsund. The German seaport of Stralsund is situated on the southern coast of a sound of the Baltic Sea that separates the island of Rugen from the mainland. This small town remained under Swedish control until 1815, when it became a part of the Prussian Province of Pomerania. Thus, Scheele was a German-Swedish pharmaceutical chemist. His birthplace was located in Ferrystreet, near the ferry harbour and the tavern Zur Fahre, the oldest pub on European continent (first mentioned in 1332). One century later, a particular speciality of Berlin, the pickled herring dish Bismarckhering, was invented in the same street. Malic acid is a bitter-tasting organic compound that is present in many sour or tart foods. One special application of malic acid is in so-called “extreme candies”, which derive their strong sour flavour primarily from the malic acid applied as a coating to the candies. The intensely sour flavour fades after few moments. The hard candy itself contains the somewhat less sour citric acid, as known from the citric acid cycle, in which malate anion is an intermediate. Malic acid was not actually named by its inventor. In 1787 Antoine Lavoisier proposed the name acide malique, which is derived from the Latin malum, meaning apple. Indeed, malonic acid (propanedioic acid, CH2(COOH)2), which can be prepared by the oxidation of malic acid, derives from the same Latin word. There is also a third acid with a similar name, maleic acid (cis-butenedioic acid, HOOC-CH=CH–COOH), which is prepared by adding water to maleic anhydride. The names of their salts or esters (malate, maleate and malonate) can be confusing, even to those experienced in chemistry. In the German language a supplemental difficulty arises; there are two different dictions for malic acid: the correct notation Apfelsaure and the older one Apfelsaure. In contrast to this confusing nomenclature, it is now quite simple to differentiate its structure. Infrared, H and C NMR spectra were given to enable structural analysis. We should first consider the mass spectrum. In the ESI mass spectrum, the molecular ions [M+Na] are seen clearly at m/z 157. The even molecular mass number of [M]=134 is a first (weak) indication of a Anal Bioanal Chem (2008) 390:1219–1220 DOI 10.1007/s00216-007-1801-2