A secondary alcohol It has the carrier carbon of the hydroxyl group (OH), attached to two carbons. While, in primary alcohol, the carbon bearing the hydroxyl group is attached to one carbon atom, and in tertiary alcohol, it is attached to three carbon atoms..
Alcohols are slightly weaker acids than water, with the following pKa: water (15.7); methyl (15.2), ethyl (16), isopropyl (secondary alcohol, 17), and tert-butyl (18) alcohols. As can be seen, isopropyl alcohol is less acidic than methyl and ethyl alcohols..
The upper image shows the structural formula for a secondary alcohol. The carbon in red is the carrier of the OH, and is linked to two alkyl (or aryl) groups R and a single hydrogen atom.
All alcohols have the generic formula ROH; but if the carrier carbon is observed in detail, then the primary alcohols (RCHtwoOH), secondary (RtwoCHOH, here raised), and tertiary (R3COH). This fact makes a difference in its physical properties and reactivity..
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The structures of the alcohols depend on the nature of the R groups. However, for secondary alcohols some exemplification can be made, considering that there can only be linear structures with or without branches, or cyclic structures. For example, you have the following image:
Note that for both structures there is something in common: the OH is linked to a "V". Each end of the V represents an equal R group (upper part of the image, cyclic structure) or different (lower part, branched chain).
This way any secondary alcohol is very easily identified, even if its nomenclature is unknown at all..
The properties of secondary alcohols physically do not differ too much from other alcohols. They are usually transparent liquids, and to be a solid at room temperature it needs to form several hydrogen bonds and have a high molecular mass.
However, the same structural formula RtwoCHOH hints at certain properties unique in general to these alcohols. For example, the OH group is less exposed and available for hydrogen bonding interactions, RtwoCH-OH-OHCHRtwo.
This is because the R groups, adjacent to the OH-bearing carbon, can get in the way and hinder the formation of hydrogen bonds. As a result, secondary alcohols have lower boiling points than primary alcohols (RCHtwoOH).
According to the Brönsted-Lowry definition, an acid is one that donates protons or hydrogen ions, H+. When this happens with a secondary alcohol, you have:
RtwoCHOH + B- => RtwoCHO- + HB
The conjugate base RtwoCHO-, alkoxide anion, must stabilize its negative charge. For secondary alcohol, stabilization is less since the two R groups have electronic density, which repels to a certain degree the negative charge on the oxygen atom..
Meanwhile, for the alkoxide anion of a primary alcohol, RCHtwoOR-, there is less electronic repulsion as there is only one R group and not two. In addition, hydrogen atoms do not exert significant repulsion, and on the contrary, contribute to stabilize the negative charge..
Therefore, secondary alcohols are less acidic than primary alcohols. If this is so, then they are more basic, and for exactly the same reasons:
RtwoCHOH + HtwoB+ => RtwoCHOHtwo+ + HB
Now, the R groups stabilize the positive charge on oxygen by giving up part of its electron density..
Hydrogen halide and phosphorus trihalide
A secondary alcohol can react with a hydrogen halide. The chemical equation of the reaction between isopropyl alcohol and hydrobromic acid, in a sulfuric acid medium, and producing isopropyl bromide is shown:
CH3CHOHCH3 + HBr => CH3CHBrCH3 + HtwoOR
And it can also react with a phosphorous trihalogen, PX3 (X = Br, I):
CH3-CHOH-CHtwo-CHtwo-CH3 + PBr3 => CH3-CHBr-CHtwo-CHtwo-CH3 + H3PO3
The above chemical equation corresponds to the reaction between Sec-pentanol and phosphorus tribromide, originating sec-pentyl bromide.
Note that in both reactions a secondary alkyl halide (RtwoCHX).
In this reaction, an H and an OH from neighboring carbons are lost, forming a double bond between these two carbon atoms. Therefore, there is the formation of an alkene. The reaction requires an acid catalyst and the supply of heat.
Alcohol => Alkene + HtwoOR
For example, we have the following reaction:
Cyclohexanol => Cyclohexene + HtwoOR
Secondary alcohols can react with metals:
CH3-CHOH-CH3 + K => CH3CHO-K+CH3 + ½ H+
Here isopropyl alcohol reacts with potassium to form the isoproxide salt of potassium and hydrogen ions..
The secondary alcohol reacts with a carboxylic acid to form an ester. For example, the chemical equation for the reaction of sec-butyl alcohol with acetic acid to produce sec-butyl acetate is shown:
CH3CHOHCHtwoCH3 + CH3COOH <=> CH3COOCHCH3CHtwoCH3
Primary alcohols are oxidized to aldehydes, and these in turn are oxidized to carboxylic acids. But, the secondary alcohols are oxidized to acetone. Reactions are usually catalyzed by potassium dichromate (KtwoCrO7) and chromic acid (HtwoCrO4).
The overall reaction is:
RtwoCHOH => RtwoC = O
Secondary alcohols are named indicating the position of the OH group in the main (longest) chain. This number precedes the name, or it can come after the name of the respective alkane for said chain.
For example, the CH3CHtwoCHtwoCHtwoCHOHCH3, is 2-hexanol or hexan-2-ol.
If the structure is cyclical, there is no need to place a numerator; unless there are other substituents. This is why the cyclic alcohol in the second image is called cyclohexanol (the ring is hexagonal).
And for the other alcohol of the same image (the branched one), its name is: 6-ethyl-heptan-2-ol.
-Sec-butanol is used as the solvent and chemical intermediate. It is present in hydraulic fluids for brakes, industrial cleaners, polishes, paint strippers, mineral flotation agents, and fruit essences and perfumes..
-Isopropanol alcohol is used as an industrial solvent and as an anticoagulant. It is used in oils and fast-drying inks, as an antiseptic and substitute for ethanol in cosmetics (for example: skin lotions, hair toners and rubbing alcohol).
-Isopropanol is an ingredient in liquid soaps, glass cleaners, synthetic flavorings in non-alcoholic beverages, and foods. In addition, it is an intermediate chemical.
-Cyclohexanol is used as a solvent, in fabric finishing, in leather processing and as an emulsifier in soaps, and synthetic detergents..
-Methylcyclohexanol is an ingredient in soap-based stain removers and specialty fabric detergents.
It is a fatty alcohol. It is a colorless liquid, slightly soluble in water, but soluble in most non-polar solvents. It is used, among other uses, in the production of flavors and fragrances, paints and coatings, inks, adhesives, home care and lubricants.
It is a steroid sex hormone. It has two hydroxyl groups in its structure. It is the predominant estrogen during the reproductive years.
It is a metabolite that probably originates from the oxidation of leukotriene lipid. It is classified as a cystinyl leukotriene. These compounds are mediators of the inflammatory process that contributes to the pathophysiological characteristics of allergic rhinitis..
It is an alcohol found in fruits. Also, it is found in ginger oil and strawberries. It is transparent, colorless and insoluble in water. It is used as a solvent for various resins and intervenes in the flotation phase in mineral processing.
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