OXYGENATED COMPOUNDS: PROPERTIES, REACTIONS, USES - CHEMISTRY - 2025

The oxygenates are those which incorporate oxygen either covalently or ionically. The best known consist of organic molecules that have CO bonds; but the family is much broader, hosting links such as Si-O, PO, Fe-O or similar ones.

Covalent oxygenates are generally organic (with carbon skeletons), while ionic compounds are inorganic, consisting essentially of oxides (metallic and non-metallic). Of course, there are many exceptions to the previous rule; but they all have in common the presence of oxygen atoms (or ions).

Bubbles of oxygen rising from the depths of the sea. Source: Pxhere.

Oxygen is easily present when it bubbles in water (upper image) or in any other solvent where it does not solubilize. It is in the air we breathe, in the mountains, in cement, and in plant and animal tissues.

Oxygenates are everywhere. Those of the covalent type are not as "distinguishable" as the others, because they have the appearance of transparent liquids or faint colors; yet the oxygen is there, bound in multiple ways.

Properties

Because the family of oxygenates is so vast, this article will focus only on the organic and covalent types.

Degree of oxidation

They all have CO bonds in common, regardless of their structure; if it is linear, branched, cyclical, intricate, etc. The more CO bonds there are, the more oxygenated the compound or molecule is said; and therefore, its degree of oxidation is higher. Being so oxygenated compounds, worth the redundancy, are oxidized.

Depending on their degree of oxidation, different types of such compounds are released. The least oxidized are the alcohols and ethers; in the former there is a C-OH bond (be this primary, secondary or tertiary carbon), and in the second COC bonds. Hence it can be argued that ethers are more oxidized than alcohols.

Following the same theme, aldehydes and ketones follow the degree of oxidation; These are carbonyl compounds, and they are so called because they have a carbonyl group, C = O. And finally, there are the esters and carboxylic acids, the latter being carriers of the carboxyl group, COOH.

Functional groups

The properties of these compounds are a function of their degree of oxidation; and likewise, this is reflected by the presence, lack or abundance of the functional groups mentioned above: OH, CO and COOH. The greater the number of these groups present in a compound, the more oxygenated it will be.

Nor can the internal COC bonds be forgotten, which "lose" importance compared to oxygenated groups.

And what role do such functional groups play in a molecule? They define its reactivity, and also represent active sites where the molecule can undergo transformations. This is an important property: they are building blocks for macromolecules or compounds for specific purposes.

Polarity

Oxygenates are generally polar. This is because oxygen atoms are highly electronegative, thus creating permanent dipole moments.

However, there are many variables that determine whether or not these are polar; for example, the symmetry of the molecule, which entails the vector cancellation of such dipole moments.

Nomenclature

Each type of oxygenated compounds has its guidelines to be named according to the IUPAC nomenclature. The nomenclatures for some of these compounds are briefly discussed below.

Alcohols

Alcohols, for example, are named by adding the suffix -ol to the end of the names of the alkanes from which they come. Thus the alcohol derived from methane, CH ₄, is called methanol, CH ₃ OH.

Aldehydes

Something similar happens for aldehydes, but adding the suffix -al. In your case, they do not have an OH group but CHO, called formyl. This is nothing more than a carbonyl group with a hydrogen bonded directly to the carbon.

Thus, starting from CH ₄ and "removing" two hydrogens, we will have the molecule of HCOH or H ₂ C = O, called methanal (or formaldehyde, according to the traditional nomenclature).

Ketones

For ketones, the suffix is ​​–ona. The carbonyl group is sought to have the lowest locator when listing the carbons of the main chain. Thus, CH ₃ CH ₂ CH ₂ CH ₂ COCH ₃ is 2-hexanone, and not 5-hexanone; in fact, both compounds are equivalent in this example.

Ethers and esters

Their names are similar, but the former have the general formula ROR ', while the latter have RCOOR'. R and R 'represent the same or different alkyl groups, which are mentioned in alphabetical order, in the case of ethers; or depending on which one is attached to the carbonyl group, in the case of esters.

For example, CH ₃ OCH ₂ CH ₃ is ethyl methyl ether. While CH ₃ COOCH ₂ CH ₃ is ethyl ethanoate. Why ethanoate and not methanoate? Because it is considered not only the CH ₃ but also the carbonyl group, since CH ₃ CO- represents the "acid portion" of the ester.

Reactions

It was mentioned that functional groups are responsible for defining the reactivities of oxygenates. OH, for example, can be released in the form of a water molecule; one speaks then of a dehydration. This dehydration is favored in the presence of heat and an acid medium.

Ethers, for their part, also react in the presence of hydrogen halides, HX. In doing so, their COC bonds are broken to form alkyl halides, RX.

Depending on the environmental conditions, the compound can be further oxidized. For example, ethers can be transformed into organic peroxides, ROOR '. Also, and better known, are the oxidations of the primary and secondary alcohols, to aldehydes and ketones, respectively.

Aldehydes, in turn, can be oxidized to carboxylic acids. These, in the presence of alcohols and an acidic or basic medium, undergo an esterification reaction to give rise to esters.

In very general terms, the reactions are aimed at increasing or decreasing the degree of oxidation of the compound; but in the process it can give rise to new structures, new compounds.

Applications

When their quantities are controlled, they are very useful as additives (pharmaceuticals, foodstuffs, in the formulation of products, gasoline, etc.) or solvents. Their uses are obviously subject to the nature of the oxygenate, but if polar species are needed then they are likely to be an option.

The problem with these compounds is that when they burn they can produce products that are harmful to life and the environment. For example, the excess of oxygenated compounds as impurities in gasoline, represents a negative aspect because it generates pollutants. The same happens if the fuel sources are vegetable masses (biofuels).

Examples

Finally, a series of examples of oxygenated compounds are mentioned:

- Ethanol.

- Diethyl ether.

- Acetone.

- Hexanol.

- Isoamyl ethaonoate.

- Formic acid.

- Fatty acids.

- Crown ethers.

- Isopropanol.

- Methoxybenzene.

- Phenyl methyl ether.

- Butanal.

- Propanone.

References

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3. Carey, FA (2008). Organic Chemistry. (6th Edition). McGraw-Hill, Interamerica, Editores SA
4. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. Amines. (10th edition.). Wiley Plus.
5. Andrew Tipler. (2010). Determination of Low-Level Oxygenated Compounds in Gasoline Using the Clarus 680 GC with S-Swafer MicroChannel Flow Technology. PerkinElmer, Inc. Shelton, CT 06484 USA.
6. Chang, J., Danuthai, T., Dewiyanti, S., Wang, C. & Borgna, A. (2013). Hydrodeoxygenation of guaiacol over carbon-supported metal catalysts. ChemCatChem 5, 3041-3049. dx.doi.org