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Alcohols are organic compounds that include one, two, or more hydroxyl groups (OH) linked to an alkyl or hydrocarbon chain’s carbon atom. Alcohols are classified as ethers and ether-like compounds.
Alcohol is also available in many shapes and forms. Alcohols are the most abundant organic compounds, constituting about one-third of organic substances. These are used as sweeteners in the manufacture of fragrances and the synthesis of other compounds. Some of these inorganic compounds are widely utilised in various industries, while others synthesise other molecules.
Alcohol may be detected using test reagents that react with the -OH group. To see alcohols, begin with a non-watery neutral liquid and add solid phosphorus (V) chloride solution. An explosion of acidic, steamy hydrogen chloride vapours indicates the presence of an alcoholic beverage. Additional tests are required to differentiate between alcohol classes.
Primary, secondary, and tertiary alcohols
Alcohols, composed of carbon(C) and hydroxyl (OH) groups, should be synthesised using a single or a single carbon atom joined straight. These alcohols include a – CH2OH group, with the OH group typically located at the end of the carbon chain.
Alcohols should have carbon atoms joined in a straight line by a hydroxyl (OH) group. The -OH group follows the CHOH group in these alcohols’ carbon chains.
In an alcohol molecule, a carbon (C) atom connected to a hydroxyl (OH) group should directly link to the other three carbon atoms. These alcohols have the -COH group, and the OH group is often found at the junction of the branching carbon chains. Calculate the quantity of alcohol present by counting the number of carbon atoms directly connected to the carbon atom bound to the OH group.
Tests for identifying tertiary alcohols
Lucas Test
It is one of the most important tests to distinguish between primary, secondary and tertiary alcohols. The reaction used is:
R-OH + HCl → R-Cl+ H20
The reaction takes place in the presence of ZnCl2.
The reaction is extremely fast for tertiary alcohols since they follow SN1 mechanism. It takes 3-4 minutes for secondary alcohols and does not occur for primary alcohols without heating. The change in solution is noticed by formation of two phases of liquids in the solution.
Thus tertiary alcohols can be differentiated from primary and secondary alcohols using this method.
The Jones test
Another technique for determining alcohol concentration is the Jones test, which employs chromium trioxide as an oxidising agent in the presence of sulfuric acid. In the presence of Jones’ Reagent, the primary alcohol enters the initial step of its transition into an aldehyde. The primary alcohol is subsequently converted to a carboxylic acid, while the secondary alcohol is converted to a ketone. The chromium oxidation state is the most critical factor to consider in this test. Jones’ Reagent contains chromium atoms with an oxidation state of +6. The presence of Cr(VI) complexes in the reagent results in a solid reddish-orange colouration of the solution.
Chromium is reduced from the oxidation state of Cr (VI) to the oxidation state of +3 — Cr during the chemical process (III). First, chromic acid and alcohol acid are combined to generate a chromate ester. The C-H alcohol link is then broken by a base, H2O, resulting in the formation of the carbonyl group and the reduction of Cr(VI) to Cr(III) (IV). The Cr(IV) receives a two-electron decrease during the reaction, while the alcohol’s carbon experiences two-electron oxidation. As a result, the reduction-oxidation phase bears its name.
Because tertiary alcohols do not react with chromium, no precipitate is formed to maintain the solution orange during the extraction process. As a result, the Jones test may help distinguish primary, secondary, and tertiary alcohols.
Test using oxidising agents
A few drops of the alcohol are introduced to a test tube holding a sodium dichromate(VI) solution that has been acidified with dilute sulfuric acid to initiate the reaction. Hot water is used to warm the tube to its working temperature.
Primary or secondary alcohol will turn the orange solution green in the presence of these chemicals. Schiff’s test will be necessary to distinguish between primary and secondary alcohols. When tertiary alcohol is used, no colour change occurs. This is because primary and secondary alcohols get oxidised but tertiary alcohols dont.
Other oxidising agents that change colour can also be used.
Applications of tertiary alcohols
Tertiary alcohols are usually used as regular alcohols in synthesis reaction. However, one of their advantage over primary and secondary alcohols is that they cannot be oxidised and hence it can be taken advantage of where oxidising agents exist in the reaction mixture.
