A buzz word in food & beverage circles, but what of its chemical functions and applications? And what of the biofuels debate? Tony Wheatly finds out.
The term 'organic' was originally derived from the word ‘organism’ and used to describe substances, compounds and molecules that were derived from either plant or animal sources and therefore the products of biological processes in the natural universe – as distinct from those extracted from inorganic materials like rocks or minerals.
The earliest attempts to synthesise organic compounds from living sources were unsuccessful. This fostered the popular belief that organic compounds were intrinsically different from inorganic compounds, in that they could only be produced in living organisms by virtue of some ‘vital force’ which they possessed.
It was Friedrich Wöhler who dispelled this myth when he discovered how to synthesize oxalic acid from cyanogen in 1824 and later in 1828, also produced urea from inorganic salts potassium cyanate and ammonium sulphate.
In recent years the term ‘organic’ has become a popular label for food items that have been produced without the use of synthetic chemical fertilizers and pesticides.
In another sense, ‘organic’ describes organisations and developments that are spontaneous in nature and have evolved with little planning or control in response to human needs.
Organic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds that contain carbon.
These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens, as well as phosphorus, silicon and sulphur.
Organic compounds are probably best described as substances containing carbon-hydrogen bonds and can be found in living organisms. Each atom of carbon has four electrons in its outer shell, enabling it to form covalent bonds with up to four other atoms including other carbon atoms.
This enables the formation of chains, branched chains and rings of carbon atoms that are the structural backbone of often very complex organic molecules.
Classification of organic compounds
A vast number of materials and substances both natural and synthetic are composed of organic compounds including: foods, furs, feathers, hides, skins, wood, paper, plastics, paints, natural and synthetic fibres, dyes, drugs, insecticides, herbicides, perfumes and flavouring agents and petroleum products.
Over six million organic compounds are known and these have been classified in various ways:
Important families of organic compounds
Functional groups are clusters of atoms recognised within organic molecules that have characteristic structures and chemical functions.
The chemical reactivity of an organic compound can be predicted from the presence of a functional group, within its molecular structure regardless of the overall size of the molecule.
It is only necessary to know about the chemistry of a few generic functions, in order to predict the chemical behaviour of thousands of real organic chemicals.
These functional groups are the sites where most of the compound’s chemical reactions occur and they are used to define organic families of compounds.
The most obvious characteristic of organic molecules or monomers is their ability to link together in groups of three or up to millions, to form large macromolecules called polymers.
The covalent chemical bonds joining covalent monomers store energy and each type of bond holds a specific amount of energy that can be measured in kilocalories per mole of the compound. This is known as potential energy and explains why many organic compounds are useful fuels.
The monomers forming a polymer can be identical, or in complex polymers such as proteins, the monomers have one or more substituted chemical groups. Virtually all macromolecules are created from a very small set of only about fifty monomers that, linked in many different configurations, yields an extremely large variety of macromolecules.
Polymers are identified by their constituent monomers and polymer chains within a substance are often not of equal length. Differing chain lengths occur because polymer chains terminate during polymerization after random intervals of chain lengthening (propagation).
Most known macromolecules are found in biology and biochemistry, in the form of long protein chains and nucleic acids such as DNA. This class of molecules are sometimes referred to as bio-macromolecules or biopolymers.
There are four classes of bio-macromolecules that perform a variety of functions in living cells:
The primary function of carbohydrates in biochemistry is that of short-term energy storage.
Carbohydrates originate as the products of photosynthesis; an endothermic reductive condensation of carbon dioxide, powered by light energy and facilitated by the pigment chlorophyll in plants.
They are the most abundant class of organic compounds found in living organisms, where they perform numerous functions.
Sugars are structurally the simplest carbohydrates and are the basic monomers that compose more complex types, notably monosaccharides, disaccharides, and polysaccharides.
The primary function of lipids in biochemistry is that of long-term storage of surplus energy, but they have many other key biological functions as structural components of cell membranes and intermediates in signalling pathways.
This diverse group of fat soluble compounds are naturally occurring and as with carbohydrates, the more complex lipids are assembled from simpler structures that are bonded together.
The primary function of proteins in biochemistry is that of building structural elements in cell membranes and muscle tissue.
The name protein, derived from a Greek word meaning primary, reflects their critical importance in the biochemistry.
They also perform vital control functions as enzymes and hormones when they act as chemical messengers. The component molecules forming proteins are called amino acids.
Proteins are organic polymers created in a condensation reaction that forms peptide bonds between the functional groups of adjacent amino acid molecules.
Once linked in the protein chain, an individual amino acid is called a residue, and the series of carbon, nitrogen and oxygen atoms is referred to as the main chain or protein backbone.
4. Nucleic acids
The primary function of nucleic acids in biochemistry is that of information storage to maintain the genetic integrity of cells in living organisms.
Nucleic acids are a family of biopolymers that are found in the cell nucleus of all living organisms and the two most common nucleic acids are Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
Each monomer, known as a nucleotide, comprises three functional groups: a nitrogenous base, a sugar, and a phosphate.
Organics and nutrition
The vital role of enzymes and hormones to sustain all life forms has been clearly established. In the context of human survival, adequate nutrition that provides the full compliment of minerals to enable our hormones and enzymes to function optimally is of critical importance.
There is a difference between the minerals available in nutritionally organic form and those derived from inorganic supplements.
Controversy abounds in the scientific community as to whether the human body can utilise inorganic minerals to support life processes.
Organic renewable energy – the
Ethanol is a type of alcohol that has been produced by fermentation of sugar cane molasses and successfully substituted for petrol since as early as 1930 in Brazil.
Due to the enormous availability of arable land, ideal climate and high efficiency achieved by the highly integrated agri-industrial infrastructure, Brazil is widely viewed as the first sustainable biofuel economy producing over 40% of the ethanol fuel used globally.
The oil price shock of 1976 motivated the initial production of ethanol from maize in the US and today, ethanol-from-corn exceeds Brazil’s output-devouring 20% of the US maize crop.
Federal subsidies that topped $8bn in 2006, backed by the endorsement of politicians in an election year, have created what is described as ‘ethanol euphoria’ delivering massive returns to farmers and producers in the so called Corn Belt.
The several practical limitations of corn-based ethanol are acknowledged in the Senate version of the energy bill that calls for a Renewable Fuels Standard of 36 billion gallons of ethanol production by 2002, of which 58% must be derived from cellulose feedstock.
Cellulosic ethanol production does avoid the greenhouse gas emissions from chemical fertiliser use, can use waste materials as feedstock, and is potentially carbon neutral, but the land use issue remains.
Biofuel production from palm oil is responsible for other kinds of environmental havoc being among the major reasons for deforestation in Indonesia and Malaysia, where tens of millions of hectares of primary forest have been destroyed – driving orangutans and other wildlife towards extinction.
During the conversion of vegetable oils to biodiesel, 10% of the output is the organic compound glycerol that during World War 1, was made commercially by microbial synthesis as feedstock for various chemicals.
This was ousted by synthesis from cheaper petrochemical feedstocks and to avoid a glut of glycerol, it has been incinerated as waste by biodiesel producers in the US and Europe.
Research led by James Dumesic at the University of Wisconsin recently devised a system to produce liquid alkanes from glycerol and water by integrating catalytic reactors, to reduce capital cost and increase thermal efficiency.
Liquid alkanes have advantages over other biofuels like ethanol, because they are of appropriate molecular weight to be used as transportation fuels components and can be transported through existing distribution infrastructure. Glycerol is also a by-product of fermentation during ethanol production and that process can be manipulated to increase the glycerol output.
Research supported by Air Products and chemicals, Inc. and the National Science Foundation has however, demonstrated a process to convert cellulose and other biodegradable organic material directly into hydrogen using microbial fuel cells.
The energy value of produced hydrogen exceeds the electrical energy absorbed, by 288%.
Hydrogen produced this way could easily be blended into natural gas for use in vehicles already adapted to that fuel. Another suggested application is the production of agricultural fertiliser by decentralised plants supplying regional demand.
Industrial organic applications
Inorganic chemical production certainly dominates in terms of bulk chemical production, but in recent years a surprising number of challenges are being addressed by organic solutions.
Among these, the application of microorganisms to treat and purify industrial effluent is delivering remarkable successes.