Synthesis of Organic Compounds

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Introduction

Organic compounds are those that are made up of carbon and hydrogen (hydrocarbons) and their derivatives. Organic compounds are the most widely spread chemical species present on earth. They are the molecules of life. All the life on this planet is dependent on various organic compounds found in the living systems.

It was thought earlier that the organic compounds could not be made in the laboratory. Scientists believed that organic compounds are special compounds that can be only made by living things in living systems. They can never be made from inorganic compounds in the laboratory. This theory was known as the Vital Force Theory. It was believed that a special force was required to make the organic compounds, found only in living organisms.

This theory was successfully rejected by Friedrich Wöhler in 1823. He was the first man to make an organic compounds Urea from inorganic compound Ammonium cyanate. Since then, millions of organic compounds have been synthesized in the laboratory. In this article, we will talk about the synthesis of organic compounds both in living systems as well as in the laboratory.

Major Organic Compounds

Millions of organic compounds have been identified and studied by chemists. IT is not possible to study the synthesis of every compound. We will limit our study to some major organic compounds found in the living systems and some others that are important in the industry.

Organic Compounds in Living Systems

Organic compounds found in living systems belong to four major classes.

  1. Carbohydrates
  2. Proteins
  3. Lipids
  4. Nucleic Acids

Organic Compounds in Industry

The following are some organic compounds that find great importance in the industry.

  1. Urea
  2. Polyethylene
  3. Polyesters
  4. Nylon

We will restrict our article to the synthesis of these organic compounds.

Synthesis in Living Systems

It means the synthesis of organic compounds by living organisms within the living structures. Under this heading, we will discuss how organisms make organic compounds in their bodies.

Carbohydrates

Carbohydrates are polyhydroxy aldehydes or ketones that serve two purposes in the living systems; provide energy for chemical processes as well as provide building blocks for complex organic compounds.

Glucose is the most important monosaccharide in living systems.

Synthesis of Glucose

Glucose can be made in the living systems in two ways; photosynthesis and gluconeogenesis.

Photosynthesis

Photosynthesis is the process by which glucose can be made from carbon dioxide and water using light energy provided by the sun. It takes place in plants, algae, and some bacteria. Such organisms that can prepare their food by themselves are called autotrophs.

Photosynthesis takes place in special organelles called chloroplasts. The process is divided into two phases; light-dependent reactions and dark reactions.

Light-dependent reactions take place on the thylakoid membranes. During these reactions, light energy is converted into chemical energy in the form of ATP and NADPH. These high energy molecules are used in the dark reactions.

During the dark reaction, the chemical energy generated in the first phase is utilized to fix carbon dioxide and water to make glucose. these reactions take place in the stroma of chloroplasts.

Photosynthesis is the process by which glucose enters the food chain. If photosynthesis does not take place, glucose can never be present in the food chain of any ecosystem. The photosynthetic organisms are therefore called the producers.

Gluconeogenesis

It is the process by which glucose can be made from non-carbohydrate sources in the living systems. It mainly occurs in the kidneys and livers of mammals. Some amino acids provide the precursors for glucose synthesis.

It is an energy-consuming process during which pyruvate is converted to glucose. Except for some initial reactions, it is a reversal of glycolysis. The first two reactions occur in the mitochondria while the rest of the process takes place in the cytosol.

Synthesis of Complex Carbohydrates

The complex carbohydrates include polysaccharides such as starch, cellulose, and glycogen. Cells make these complex carbohydrates by combining the glucose molecules.

Glycogen is made by animal cells by a process called glycogenesis.

Starch is made by plant cells. Its synthesis goes side by side with the photosynthesis.

Cellulose is also made by plant cells. It is an important component of the plant’s cell walls.

Proteins

Proteins are the polymers of amino acids. They make up more than 50% of the total weight of living organisms.

Synthesis of Amino Acids

Amino acids are the precursors for protein synthesis. They are divided into two categories;

  • Essential Amino acids
  • Non-essential amino acids

Essential amino acids cannot be made in the human body and are must be obtained from the diet. They are made by other living organisms using precursors such as acetic acid and pyruvic acid.

Non-essential amino acids are those that can be made in the human body. They are synthesized from precursors of glucose metabolism. Some examples are as follows;

  • Alanine is made from pyruvate
  • Glutamine is made from alpha-ketoglutarate
  • Glutamine is made from glutamate
  • Aspartate is made from oxaloacetate

They can also be made from other precursors like phenylalanine, threonine, etc.

Synthesis of Proteins

Recall that proteins are the polymers of amino acids. They are made in a process called translation.

The information for protein synthesis is carried by the mRNA from the nucleus to the cytoplasm. The mRNA molecules are read by the tRNA on the surface of ribosomes. Amino acids for protein synthesis are carried by the tRNA molecules and are inserted into the growing polypeptide chain. The sequence of amino acids in the polypeptide chain is dictated by the nucleotide sequence in mRNA.

The polypeptide chains thus made are further processed in the rough endoplasmic reticulum. Here the proteins undergo folding and other structural modifications.

The proteins that are destined to be sent out of the cell are further processed in the Golgi vesicles. Here, they are packed into membrane-bound vesicles and are sent towards cell membrane for exocytosis.

Proteins that are to be used in the cytoplasm are dumped into it. Those needed in mitochondria or other organelles are transported via transport vesicles.

Lipids

It is a group of heterogeneous organic compounds. Lipids vary greatly in their structure, occurrence, and properties. Therefore, the synthesis of lipids also shows a great variety.

Synthesis of Triglycerides

Triglycerides are the most abundant acylglycerols. They are made up of two components; fatty acids and glycerol.

  • Fatty acids are synthesized in the body by combining acetic acid molecules. acetic acid is obtained from pyruvate that comes from glucose.
  • Glycerol is three-carbon alcohol that can be synthesized from glyceraldehyde-3-phosphate, an intermediate in glycolysis.

The two components are joined to form triacylglycerols in a process called esterification.

Synthesis of Phospholipids

Phospholipids consist of alcohol that is attached to either a molecule of diacylglycerol (DAG) or sphingosine. There are two categories of phospholipids; glycerophospholipids and sphingolipids.

Glycerophospholipids have glycerol as alcohol. Phosphatidic acid is the precursor of all these phospholipids. It is made by adding a phosphate group to the third carbon of glycerol in diacylglycerol. The rest of the glycerophospholipids are made from it via various modifications.

Sphingophospholipids are made from amino alcohol, sphingosine. A fatty acid is attached to sphingosine via an amide linkage to form ceramide. This ceramide is used as a precursor for the synthesis of various sphingolipids like sphingomyelin.

Synthesis of Glycolipids

It is another important category of lipids having sphingosine. They consist of two components; a lipid component called ceramide and a carbohydrate component that could be monosaccharide or disaccharide etc. Besides, acids like N-acetyl neuraminic acid or charged groups like phosphate groups may also be present, attached to the ceramide.

All the glycolipids are synthesized by adding the required monosaccharide, disaccharide, acid, or any other group to the ceramide. Ceramide itself is made by adding a molecule of fatty acid to sphingosine via an amide linkage.

Nucleic Acids

Nucleic acids are the polymers of nucleotides. They include DNA and RNA. Nucleic acids are synthesized in the living cells by a process called replication. During this process, nucleotides are used as precursors to make polynucleotide chains. The sequence of nucleotides in the chain is guided by the parent DNA strand. the process is carried out by enzymes called polymerases.

  • New DNA is made from parent DNA in a process called DNA replication. The major enzyme involved in this process is DNA polymerase.
  • The synthesis of RNA from DNA is called transcription. RNA polymerases are responsible for this process.

As nucleotides are precursors for both DNA and RNA, the structure of the synthesis of these compounds is important to be mentioned.

Synthesis of Nucleotides

 Each nucleotide is made up of three components;

  • A pentose sugar (ribose or deoxyribose)
  • A nitrogenous base (purine or pyrimidine)
  • One or more phosphate groups

Pentose sugar is made from glucose. Ribose is formed as an intermediate in the pentose-phosphate pathway of glucose. It can be deoxygenated to form deoxyribose.

The nitrogenous base is constructed on the ribose sugar in the process of purine or pyrimidine synthesis. During this process, the nitrogenous base is made by using atoms donated by carbon dioxide and some amino acids like glycine.

The phosphate group is added to the sugar before the synthesis of the base. It is donated by a molecule of ATP.

Synthesis in Industry

 Since the rejection of Vital Force theory, millions of organic compounds have been artificially synthesized in the laboratory. These compounds are of great value as they are being used by humans in daily life. They play an important role in the welfare of mankind.

Under this heading, we will discuss the synthesis of some important organic compounds in the industry.

Synthesis of Urea

Urea is an important fertilizer that is being used worldwide in the agriculture industry. It makes crops grow faster by providing nitrogen to plants, an important nutrient.

Urea is an organic compound found in the urine of mammals. Animals make urea from ammonia during the urea cycle. It is an important means for animals to get rid of toxic ammonia gas.

In the industry, urea is made from two inorganic gases; carbon dioxide and ammonia. The synthesis of urea is a two-step process;

  1. In the first step, ammonia and carbon dioxide react to form ammonium carbamate. This reaction takes place in a reactor having 150 bar pressure and a temperature around 210 oC.
  2. The ammonium carbamate thus formed is subjected to dehydration in the next step. As a result, urea is formed.

The urea solution thus obtained is subjected to the purification process. During this phase, the urea solution is evaporated, and the resultant vapors are collected and crystallized to form pure urea crystals.

The urea crystals are packed and dispatched.

Synthesis of Polyethylene

Polyethylene is a synthetic organic compound used in the packaging industry. It is used to make plastic bags, packaging films, plastic toys, bottles and cable insulations, etc.

Polyethylene is a polymer of ethylene, a simple hydrocarbon having two carbon atoms. It is an unsaturated hydrocarbon belonging to the class of alkenes. Its general formula is (C2H4)n where n is in thousands.

Polyethylene is made from ethylene or ethene in a process of polymerization. During this process, the ethylene monomers are continuously being added to one another in the presence of a catalyst. Two types of catalysts that are used during this process are as follows;

  • Ziegler-Natta
  • Metallocene

Various types of polyethylene are being made. They differ in structure and properties. The different types are made by some modifications in the manufacturing process.

One major disadvantage of polyethylene is that it is not biodegradable. Due to this reason, it poses some serious threats to the environment. It is considered one of the major causes of environmental pollution. Environment protection societies working worldwide are now proposing to ban on polyethylene use. Many countries have also banned the use of polyethylene.

Synthesis of Polyesters

It is another group of synthetic organic compounds. They are used in the fabric industry to make jackets, trousers, shirts, bedsheets, and other types of clothing. They are also used to make ropes, yarns, belts, etc. Polyesters find their importance in several industries worldwide.

Polyesters are the polymeric compounds having ester groups in their chain. Different types of polyesters are being made based on the groups in them other than the ester linkage.

Polyester can be made by a simple reaction between a dicarboxylic acid and a dialcohol.

Different methods are used to make polyesters at the industrial scale. Some of the methods are as follows;

  • Polycondensation
  • Azeotrope esterification
  • Alcoholic transesterification

Synthesis of Nylon

Nylon is another synthetic organic compound used in the fabric industry. It a widely used artificial fiber for making shirts, trousers, curtains, sheets, and other items of clothing. It has some silky feel.

Nylon is an artificial organic compound belonging to the class of thermoplastics. It is a polymer of hexamethylenediamine and adipic acid. It is synthesized in the industry by a polycondensation reaction during which equal amounts of the two components are added to a reaction chamber.

This reaction gives molten Nylon which can be further converted into granules or converted into fibers. Nylon fibers are used for various purposes. They are also used to make stitches used in hospitals.

Summary

Organic compounds are the molecules associated with life. Earlier, it was thought that they cannot be made in the laboratory. However, now they are being made in the industry from inorganic compounds.

Livings systems remain the most important source of organic compounds like carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates include simple sugars like glucose and complex carbohydrates like starch.

  • Glucose is made by the process of photosynthesis or gluconeogenesis
  • Complex carbohydrates are made by combining glucose residues

Lipids include a vast variety of organic compounds that can be synthesized in various ways.

  • Phosphatidic acid is made from glycerol and fatty acids
  • Glycerophospholipids are made by using phosphatidic acid as a precursor
  • Sphingophospholipids are made by using ceramide as a precursor.
  • Glycolipids are made by adding carbohydrates, acids or ionic groups like phosphate or sulfate group ceramide

Proteins are made by combining amino acids in a special sequence guided by mRNA. Amino acids can be made in the body from different sources or can be obtained in the form of diet.

Nucleic acids are made from nucleotides. Nucleotides themselves are obtained by processing the ribose sugar which comes from the pentose-phosphate pathway.

Synthetic organic compounds are being made in the industry for the welfare of mankind. These include urea, polyethylene, polyesters, nylon, etc.

Urea is made from carbon dioxide and ammonia. The urea solution is evaporated and crystallized to form pure granules.

Polyethylene is made by polymerizing ethylene under special conditions in the presence of a catalyst.

Polyesters can be made by three different processes;

  • Polycondensation
  • Azeotrope esterification
  • Alcoholic transesterification

Nylon is made by polymerizing the two components in an equal ratio. A molten substance is obtained which is then spun to make nylon fibers.

References

  1. Stryer, Lubert (1995). Biochemistry (fourth ed.). New York – Basingstoke: W. H. Freeman and Company. ISBN 978-0716720096
  2. Viers, Brendt D. (1999). Polymer Data Handbook. Oxford University Press, Inc. p. 189. ISBN 978-0195107890
  3. Palmer, Robert J. (2001). “Polyamides, Plastics”. Encyclopedia Of Polymer Science and Technology (4th ed.). John Wiley & Sons, Inc. doi:10.1002/0471440264.pst251.