Iron sulfite medium

There are a number of other media suitable for the growth of clostridia. The most important are Reinforced Clostridial Medium (RGM), Iron Sulfite medium, and Thioglycollate medium. The aim of all these media is to provide an environment of sufficient reducing power to allow anaerobes to grow in the presence of air. Anaerobes will grow on many media if cultured in an anaerobic jar, but this is not a simple process and should be avoided if possible. 

Synthetically useful routes to dibenzo[c,e J[l,2]dithiins are normally based on cyclizations of biphenyI-2,2 -disulfonyl chlorides. A method applied successfully to the parent compound reduces the precursor with zinc in acetic acid to generate the bis thiol, which is then gently oxidized to the dithiin using iron(II) chloride (66HC(21-2)952). An alternative one-step reductive cyclization, which has been applied to the preparation of the 2,9- and 3,8-dinitro derivatives, involves reduction of the appropriate bis sulfonyl chlorides with hydriodic acid in acetic acid (68MI22600). Yet another reductive cyclization uses sodium sulfite followed by acidification, and these conditions lead to dibenzo[c,e][1,2]dithiin 5,5-dioxide. The first step of the reaction is reduction to the disodium salt of biphenyl-2,2 -disulfinic acid which, on acidification, forms the anhydride, i.e. dibenzo[c,e][l,2]dithiin 5,5,6-trioxide. This is not isolated, but is reduced by the medium to the 5,5-dioxide (77JOC3265). Derivatives of dibenzo[c,e] [1,2]dithiin in oxidation states other than those mentioned here are obtainable by appropriate oxidation or reduction reactions (see Section 2.26.3.1.4). 

In a synthetic medium, SO2 has been shown to take several days to consume 8.0-8.6 mg of oxygen per liter (this amount corresponds with the saturation of this medium). Such oxidation requires the presence of catalyzers, notably iron and copper ions. Yet musts are very oxidizable and should therefore be rapidly and effectively protected against oxidation. Sulfiting accomplishes this. Sulfur dioxide, however, cannot act by its anti-oxygen effect, that is to say by combining with oxygen which is no longer available for the oxidation of other must constituents. 

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