In this section a question and answer summary is given about the structure of humic acid molecules. For a full explanation of these answers please refer to the section entitled “Structure and Origin of Humic Acids and their Relationship to Kerogen, Bitumen, Petroleum and Coal.”
Q Are there many humic acid molecules?
A Yes, probably thousands (complexity like components in petroleum).
Q When one sees complex published structures containing many aromatic groups and links, are they correct?
A No, they do not resemble humic acid molecules.
Q What are the molecular weights of humic acids?
A In the vicinity of 800 – 1200 amu (unaggregated).
Q What structures do humic acid molecules contain?
A These structures:
Q Is the exact polymeric structure of any humic acid molecule known?
A No, but these can be postulated as major structures, either by themselves or with other groups listed above present in the chain:
A Are there minor polymeric components?
Q Yes, these have been found:
C17-C30 alkanes, considered to be degradation (probably decarboxylation) products
R[CH2CH2]n-H where R = C18H37O4
C20H40N305[(CH2)mO]n-H where m = 2 or 3 and n = 1-3
Q Are there minor non-polymeric components?
A Yes, such as succinic, maleic, oxalic and ketoglutaric acids. Minor amounts of aromatic acids such as vanillic and syringic acids in terrestrially-derived humic acids are considered to be contaminants.
Q Does the humic acid molecule change structure with the environment?
A Yes, there are two major structural changes. The gem-diol group present in the solid can lose a molecule of water on dissolution in certain solvents or at different concentrations in a given solvent. Also, the conjugate chelate group can change its equilibrium between an enol-keto and di-keto group, depending on the solvent and concentration. A minor keto-enol change may also occur.
Q What effect does the dynamic nature of the humic acid molecule as described above have on the properties of humic acids?
A A single molecule changes its structure and chemistry eternally, and is therefore very difficult to analyze, and gives the impression that humic acids are composed of an infinite variety of molecules.
Q Can the structure of underivatized humic acids be determined?
A Probably not, because of the dynamic nature of humic acid molecules described above.
Q What are the best humic acid derivatives?
A Butylated derivatives; butylated plus lactonized derivatives; reduction with Raney Nickel or lithium aluminium hydride followed by acetylation or derivatization with pentafluoropropionic anhydride.
Q What are the best techniques for investigating the structure of derivatized humic acids?
A Fluorescence and solution FTIR. HPLC-MS, FT-MS and NMR are also useful, but only for the most hydrophobic derivatives.
16-12
Hello, it really interesting, thanks
Comment by ShealaGag — 2009 @ 10:49 pm
Hello Marc
I have not been able to decarboxylate humic acids to petroleum. By heating humic acids at about 220 deg C with a mixture of sodium hydroxide and calcium oxide it is easy to decarboxylate them. Also, in butylation reactions with n-butanol and sulfuric acid catalyst I obtained decarboxylated products. However, I always obtained black solids similar to coal, that I believe were humin.
Humic acids are composed of many types of compounds, and most of these compounds contain the conjugate chelate carbonyl group that changes structure with the environment and is difficult to do anything with. I believe that there are some humic acid structures that do not contain this group and are related to the fulvic acids, and on decarboxylation they may give petroleum.
Regards
Michael
Comment by humicacid — 2009 @ 10:48 am