In this article we will consider the phenomenon of oxidation. This is a multi-component concept that appears in various fields of science, such as biology and chemistry. We will also get acquainted with the variety of this process and its essence.
Introduction
From the basic and original point of view, oxidation is a process of a chemical nature, which is accompanied by an increase in the degree of atomic oxidation of the substance that undergoes it. This phenomenon occurs due to the transfer of electrons from one atom (reductant and donor) to the second (acceptor and oxidizer).
This terminological unit was introduced into the circulation of chemistry at the beginning of the 19th century, and Academician V. M. Severgin to create a designation indicating the interaction of substances with oxygen from atmospheric air.
In some cases, the oxidation of a molecule is accompanied by the creation of instability in the structure of the substance and leads to its decay into molecules with greater stability and small sizes. The fact is that this process can be repeated at several different levels of grinding. That is, the smaller particle formed can alsohave a higher degree of oxidation than the atomic particles that were the original in the same substance, but larger and more stable.
In chemistry there is the concept of the lowest and highest degree of oxidation. This allows us to classify atoms according to their ability to exhibit this property. The highest oxidation state corresponds to the number of the group in which the element is located. The lowest degree, as a rule, is determined by the correspondence of an even and an odd number: the highest 8=the lowest 2, the highest 7=the lowest 1.
Combustion
Combustion is an oxidation process. In atmospheric air (as well as in an environment of pure oxygen) they can be oxidized in the form of combustion. A variety of substances can serve as an example: the simplest elements of substances of metals and non-metals, inorganic and organic compounds. However, the most practically significant is the combustible substance (fuel), among which are the natural reserves of oil, gases, coal, peat, etc. Most often they form from a complex mixture of hydrocarbons with a small proportion of oxygen, sulfur, nitrogen-containing organic compounds, as well as trace inclusions of other elements.
Biological oxidation
In biology, oxidation reactions are processes that together converge to a change in the oxidation state of the atoms involved in the reaction, and this happens due to the electronic distribution between the interacting components.
The first assumption is that in all living organisms the most complex chem. reaction, was put forward in the eighteenthcentury. The French chemist A. Lavoisier studied the problem. He drew attention to the fact that the course of combustion and oxidation in biology are similar to each other.
Scientists have made a study of the path of oxygen that was absorbed by a living being due to breathing. They reported that these oxidation processes are similar processes occurring at different rates. He drew attention to the decomposition process, which, as it turned out, is based on the phenomenon of the interaction of an oxygen molecule (oxidizing agent) with an organic substance that includes carbon and/or hydrogen atoms. As a result of decomposition, an absolute transformation of matter occurs.
There were moments of the process that scientists could not fully understand, including questions:
- For what reason is oxidation carried out under conditions of low body temperature, despite its presence outside the body, only at high temperature.
- For what reason, oxidation reactions are phenomena that are not accompanied by the release of a flame, as well as huge releases of released energy.
- How is the "burning" of the nutrient range of substances in the body, if it is 80% (approximately) composed of liquid - water H2O.
Types of biological oxidation
According to the conditions of the environment in which oxidation occurs, it is divided into two types. Most fungi and micro-organisms obtain energy resources by converting nutrients through an anaerobic process. This reactionoccurs without access to molecular oxygen, and is also called glycolysis.
A more complex way of converting nutrients is the aerobic form of biological oxidation or tissue respiration. The lack of oxygen causes the cells to fail to oxidize for energy and they die.
Getting energy by a living organism
In biology, oxidation is a multicomponent phenomenon:
- Glycolysis is the initial stage of heterotrophic organisms, during which monosaccharides are cleaved without oxygen, and it precedes the start of the process of cellular respiration.
- Pyruvate oxidation - conversion of pyruvic acids into acetylcoenzyme. These reactions are possible only with the participation of pyruvate dehydrogenase enzyme complexes.
- The process of decomposition of beta-fatty acids is a phenomenon carried out in parallel with the oxidation of pyruvate, the purpose of which is the processing of each fatty acid into acetylcoenzyme. Further, this substance is supplied to the tricarboxylic acid cycle.
- Krebs cycle - the conversion of acetylcoenzyme into citric acids and further exposure to subsequent transformation (phenomena of dehydrogenation, decarboxylation and regeneration).
- Oxidative phosphorylation is the last step in the transformation in which a eukaryotic organism converts adenosine diphosphate to adenosine triphosphoric acids.
It follows that oxidation is a process involving:
- phenomenonremoval of hydrogen from the substrate, which undergoes oxidation (dehydrogenation);
- substrate electron recoil phenomenon;
- the phenomenon of the addition of an oxygen molecule to a substrate.
Reaction over metals
Oxidation of a metal is a reaction during which, through the interaction of an element from the group of metals and O2, oxides (oxides) are formed.
In a broad sense, a reaction in which an atom loses an electron and creates various compounds, for example, substances of chlorides, sulfides, etc. In the natural state, most often metals can only be in a completely oxidized state (in the form of ore). It is for this reason that the oxidation process is presented as a reduction reaction of various components of the compound. Practically used substances of metals and their alloys, when interacting with the environment, gradually oxidize - they undergo corrosion. Metal oxidation processes occur due to thermodynamic and kinetic factors.
Valence and oxidation
The oxidation state is the valency. However, there is some difference between them. The fact is that the valency of chem. element man determines the ability of an atom to establish a certain number of chemical bonds with other types of atoms. This is due to the presence of different types of atom, respectively, different ability to create a relationship. However, valence can only be in a covalent compound and is formed due to the creation of a common electron pair between atoms. Degreeoxidation, in contrast to valence, is the degree of conditional charge that an atom of a substance possesses. It can be positive "+", zero "0" and negative "-". Also, the oxidation state suggests that all bonds in a substance are ionic.
Reaction over water
More than two billion years ago, plant organisms took one of the most important steps towards the beginning of evolution. The process of photosynthesis began to take shape. However, initially only reduced substances of the hydrogen sulfide type were subjected to photooxidation, which were present on earth in extremely small sizes. Water oxidation is a process that introduced a significant amount of molecular oxygen into the atmosphere. This allowed bioenergy processes to move to a new aerobic level. The same phenomenon allowed the formation of an ozone shield that protects life on Earth.
