Question

Write the equation for the complete hydrogenation of the polyunsaturated fatty acid linoleic acid, \(CH_{3}\left(CH_{2}\right)_{4} CH=CH H_{2} CH=CH\left(CH_{2}\right), COOH\) .

Short answer

The complete hydrogenation of linoleic acid can be represented by the equation: \[CH_3(CH_2)_4CH=CHCH_2CH=CH(CH_2)_7COOH + 2H_2 \rightarrow CH_3(CH_2)_4CH-CHCH_2CH-CH(CH_2)_7COOH\]

Step-by-step solution

Identify the double bonds

We need to find the double bonds in the structure, which are the ones we will hydrogenate. In linoleic acid, there are two carbon-carbon double bonds. Let's rewrite the formula highlighting the double bonds: \[CH_3(CH_2)_4\underline{CH=CH}CH_2\underline{CH=CH}(CH_2)_7COOH\]

Add hydrogen molecules across the double bonds

We will now add hydrogen molecules across each of the double bonds to turn them into single bonds. To do this, we will need 2 mole of hydrogen gas, \(H_2\). The hydrogenated product will have the double bonds replaced with single bonds: \[CH_3(CH_2)_4CH-CHCH_2CH-CH(CH_2)_7COOH\]

Write the complete hydrogenation equation

Now we can put everything together and write the complete hydrogenation equation, remembering to balance it with the appropriate number of hydrogen molecules required: \[CH_3(CH_2)_4CH=CHCH_2CH=CH(CH_2)_7COOH + 2H_2 \rightarrow CH_3(CH_2)_4CH-CHCH_2CH-CH(CH_2)_7COOH\] This is the equation for the complete hydrogenation of linoleic acid.

Key concepts

Chemical Reactions

Chemical reactions are the backbone of chemistry, involving the transformation of substances through the breaking and forming of bonds between atoms. In the context of the hydrogenation of linoleic acid, a specific type of chemical reaction called an addition reaction is applied. During this process, hydrogen molecules (\(H_2\)) are added across the carbon-carbon double bonds present in the linoleic acid structure, converting them into single bonds.
This alteration fundamentally changes the physical and chemical properties of the substance. Notably, in the case of linoleic acid, which is a polyunsaturated fatty acid, hydrogenation increases saturation, leading to a more solid form at room temperature. The following equation exemplifies the chemical reaction of the hydrogenation of linoleic acid:
\begin{align*}CH_3(CH_2)_4CH=CHCH_2CH=CH(CH_2)_7COOH + 2H_2 \ \rightarrow CH_3(CH_2)_4CH-CHCH_2CH-CH(CH_2)_7COOH.d{align*}In order to accomplish this reaction, a catalyst such as nickel is often used to accelerate the process and improve efficiency.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds and their properties. Essentially, it deals with a vast array of molecules built primarily from carbon atoms. Linoleic acid, the subject of our exercise, is one example of an organic compound. It is specifically classified as a polyunsaturated fatty acid.

Structure and Reactivity

In organic chemistry, the structure of a molecule significantly influences its reactivity. Linoleic acid contains carbon-carbon double bonds, indicative of unsaturation, which are much more reactive than single bonds. This reactivity is what allows linoleic acid to undergo hydrogenation, as the double bonds easily break to accommodate the addition of hydrogen atoms.

Catalysts in Organic Reactions

Catalysts, such as nickel, serve a principal purpose in many organic reactions, including hydrogenation. They provide a surface where reactants can come together to react more readily without being consumed in the process, which is crucial for the enhancement of reaction rates and yield.

Saturation of Unsaturated Fatty Acids

Unsaturated fatty acids like linoleic acid contain one or more double bonds between carbon atoms. These double bonds can make the fatty acids fluid and liquid at room temperature. The concept of saturation refers to the addition of hydrogen atoms to these double bonds.

From Liquid to Solid

When unsaturated fatty acids undergo hydrogenation, the double bonds are converted to single bonds, and the molecule becomes more 'saturated' with hydrogen. This process increases the melting point of the fatty acid, resulting in a transition from liquid to a more solid state, which is often desired in food products like margarine.

Implications for Health and Industry

Saturated fats, which result from full hydrogenation, have different health implications compared to their unsaturated counterparts. While they can prolong shelf life and provide certain textures in food, they have also been associated with health concerns, leading to the consideration of partial hydrogenation as an alternative to strike a balance between health and functionality.
Understanding the chemistry behind the saturation of unsaturated fatty acids is not just academically intriguing but also has practical significance in nutrition, food science, and industrial applications.