Biological Reactions of Organic Carbon
  1. Hydrocarbon Oxidation

    2. Oxidation of organic carbon compounds may be classified into two main types of reactions.

    The first is the oxidation of hydrocarbons. This oxidation occurs in a multi-step process. The first step is the oxidation of a terminal, or a carbon

    Acid formation is more common than that forming the ketone. These reactions probably involve intermediates (alcohols and aldehydes) and may involve H2O, H+, and e-.

    The next step removes the acid and the second, or b carbon, through a processes call "b-oxidation"

    b-oxidation may continue until the hydrocarbon is converted to CO2 and H2O.

    b-oxidation requires labile bonds on the b carbon. Subsequently, branched hydrocarbons are not oxidized as rapidly.

    Biological Reactions of Organic Carbon
  2. Aromatic Oxidation

    3. The primary step of aromatic compound oxidation occurs by an epoxidation

    The epoxide may rearrange to the phenol in the hydroxylation reaction

    or may be further oxidized to acids or ketones

     

    Products in the oxidation of naphthalene by the fungus Cunninghamella elegans are shown below. These products can be explained by initial epoxidation of the 1 and 2 carbons.

    Notice that more than one oxidation is required to produce some of these products.

    Biological Reactions of Methane

    Methane (CH4) production and oxidation by microorganisms is important to the understanding of the global carbon cycle. Microorganisms are thought to produce about 80% of the atmospheric methane.

    Methane is produced in very low pE (reducing) environments under anaerobic oxygen-free conditions by bacterial decomposition of organic materials.

    The methane-forming (methanegenic) bacteria convert carbon dioxide to methane

    where the carbon dioxide comes from organic carbon

    Overall, the combination of these two reactions is

    The methanegenic bacteria are anaerobic. They die in oxygen.

    They significantly reduce the BOD by the production of methane.

    Since

    and since CH4 is a gas which is vented from the water, each mole of CH4

    gas produced reduces the oxygen demand by 2 moles.

    More Biological Reactions of Organic Carbon
  3. Hydrolysis - Hydrolysis involves the addition of water to a relatively labile bond accompanied by cleavage into two products.

    4. One of the resulting compounds is protonated while the other is hydroxylated.

    Hydrolysis is promoted by hydrolase enzymes. Esters (R-C=O-OR’), amides (R-C=O-NHR’), and their analogs are labile to hydrolysis.

  4. Organic Reduction - Biological reduction occurs via reductase enzymes. Table 6.2 gives some examples.
  5. Dehalogenation – These reactions are nucleophilic substitutions of OH- for the halides; I-, Br-, Cl-, and to a lesser extent, F-.

    6. Microorganism dehalogenation does not always produce the alcohol, but rather the alcohol, if it exists, is reduced to the hydrocarbon

    Fluorocarbons are particularly difficult to defluorinate due to the high C-F bond strength. This bond is generally stronger than the C-H bond.

  6. Dealkylation – These reactions involve the removal and oxidation of an alkyl group attached to a labile bond. It is similar to hydrolysis.

Last updated Thursday, December 21, 2006

This page was last edited Thursday, December 21, 2006