An Investigation of the Metallic Derivatives of Ortho-Substituted Azo Compounds

Boyle, James L (1939) An Investigation of the Metallic Derivatives of Ortho-Substituted Azo Compounds. PhD thesis, University of Glasgow.

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The investigation of the mono-o-hydroxyazo compounds showed that these compounds formed metallic derivatives with comparative ease. This seems to be in accord with the concensus of published work on the subject, though disputed by some of the foremost investigators. An interesting point that arose, was that copper seems unable to form a complex with mono-o-hydroxyazo sulphonic acids, unless the sulphonic acid group has been neutralised. In this respect, this class is inferior in lake forming properties to the di-o-hydroxyazo compounds. It appears that, in general, with o:o'-dihydroxyazo compounds metallisation results in the formation of typical inner complex compounds, both hydroxyl groups acting as acidic groups and either one or both of the azo nitrogen atoms co-ordinating with the metal. However, the experiments have led also to the conclusion that, several different derivatives of the same metal can be prepared from the one dyestuff; the differences being in the proportion of metal combined with the dyestuff and being accounted for by one of the following reasons; free sulphonic acid group; metal retaining within the complex some residual basicity; some of the hydroxyl groups may not have combined with the metal through hydrogen replacement, but merely by co-ordination. The experiments with primary and secondary complexes leads to the following suggested mechanism for the conversion of one to the other. Primary complexes contain monobasic chromium. The first reaction in the passage of a primary into a secondary complex is the formation of the free sulphonic acid of the former and this combines with the monobasic chromium already in the complex to give an even more internally bound inner complex salt. The above represents the suggested course of the change. When taking into account the co-ordinate links between the metal and the azo nitrogen atoms, it is apparent that a compound represented as the secondary one is, would be linked to the dyestuff molecule at five points. Such quinquidentate chelate compounds do not seem to have been recorded in the literature hitherto. The claims in the patent literature were confirmed that an o-alkyloxy group can give rise to metallic derivatives, if the conditions of the reaction are such as first to hydrolyse the alkyloxy group. This can be done by metallising under pressure - a method which was found to facilitate complex formation and to encourage the maximum combination between dyestuff and metal. In the o-carboxyl-o-hydroxyazo compounds, it was found that an o-carboxyl group, though it resembles an o-hydroxyl, results in the formation of a slightly less stable link between the azo compound and the metal. The experiments with toluylene Brown G indicated that an amino group o-to the azo link acts similarly to an hydroxyl group, i.e. by hydrogen displacement displacement it can combine with copper or chromium forming part of a chelate group and there were no signs of triazol formation. The reactions of Chrome Brown T.V. (in which there is both an o-amino and an o-hydroxyl group) supported this conclusion. The test with the Grignard Reagent showed that chromium lakes sometimes contain the metal in a monobasic state.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1939
Depositing User: Enlighten Team
Unique ID: glathesis:1939-80176
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 02 Mar 2020 23:02
Last Modified: 02 Mar 2020 23:02

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