chemical synthesis
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What is chemical synthesis?
Chemical synthesis involves constructing complex chemical compounds from simpler ones, a process crucial for obtaining many substances essential to daily life. It is applied to all types of chemical compounds but is most often used with organic molecules.
Chemists synthesize natural chemical compounds to better understand their structures, and they also produce compounds that do not occur naturally for research. In industry, chemical synthesis is used to make products in large quantities, such as ammonia for fertilizers and vinyl chloride for PVC plastic. Robert B. Woodward was known for total synthesis, creating organic substances from simple starting materials.
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Why do scientists perform chemical synthesis?
Scientists perform chemical synthesis for three main reasons:
- To meet industrial demands for products like ammonia, fertilizers, and PVC plastics
- To determine the structure of naturally occurring compounds such as proteins and alkaloids
- To create non-natural compounds with specific structures to examine their properties and test chemical theories
By synthesizing compounds, chemists can gain a better understanding of their structures and produce compounds for research purposes that do not form naturally. In industry, synthesis is used to make products in large quantities.
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What basic materials are needed for a chemical synthesis?
Chemical synthesis involves constructing complex chemical compounds from simpler ones, a process vital for producing many substances essential to daily life.
Key materials needed include:
* Reactants At least two different substances are needed. These react when brought into close proximity, typically in liquid or gaseous states, or in a solution if they are solids.
* Solvents These are used to dissolve materials to form a solution. They can be polar (like water) or nonpolar (like hydrocarbons).
* Catalysts These can speed up or slow down a reaction.
* Energy This is often required to initiate the reaction, such as heat, radiation, or electric current.4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do scientists choose which chemicals to combine in a synthesis?
Scientists strategically select chemicals for synthesis based on several factors. When planning a chemical synthesis, chemists start with the end product in mind and work backward to identify simpler compounds. They consider the cost and availability of starting materials, the energy needed for the reaction, and the expense of separating and purifying the end products.
Knowledge of the reaction mechanism and the behavior of functional groups helps determine the most favorable pathway to the desired product. Chemists aim for reactions that affect only one part of the molecule, maximizing the yield of the desired product in the shortest time possible. Competing reactions and the formation of by-products are also important considerations.
To facilitate the reaction, substances are often in liquid or gaseous states, or in a solution if they are solids. Temperature plays a crucial role, as reaction rates generally increase with temperature, though catalysts are used when heating is insufficient or impractical.
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What are some common examples of chemical synthesis in everyday life?
Chemical synthesis is the creation of complex chemical compounds from simpler ones and is used to produce many substances important to daily life.
Common examples:
* Fertilizers Ammonia, synthesized from nitrogen and hydrogen, is used to make ammonium sulfate, a fertilizer.
* Plastics Vinyl chloride is made from ethylene and is used to produce polyvinyl chloride (PVC) plastic.
* Soap Soap is made through the saponification reaction of natural fats or oils with a hot caustic alkali solution, such as sodium hydroxide.
* Synthetic detergents Anionic-active synthetic detergents are made through the industrial process of sulfonation, where a sulfo group is attached to a long carbon chain.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do scientists control the conditions (like temperature or catalysts) to get the desired product in a chemical synthesis?
In chemical synthesis, scientists manipulate conditions such as temperature and catalysts to steer reactions toward desired products.
To increase reaction rates, chemical syntheses are often conducted at higher temperatures. However, if heating alone is insufficient or reactants are unstable, catalysts are employed. Catalysts can accelerate or decelerate a reaction.
Fine-tuning reaction conditions is crucial, especially for rapid or violent reactions. For instance, in polyethylene synthesis from ethylene gas, heat release must be controlled to prevent decomposition into carbon and hydrogen.
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chemical synthesis, the construction of complex chemical compounds from simpler ones. It is the process by which many substances important to daily life are obtained. It is applied to all types of chemical compounds, but most syntheses are of organic molecules.
Chemists synthesize chemical compounds that occur in nature in order to gain a better understanding of their structures. Synthesis also enables chemists to produce compounds that do not form naturally for research purposes. In industry, synthesis is used to make products in large quantity.
Chemical compounds are made up of atoms of different elements, joined together by chemical bonds. A chemical synthesis usually involves the breaking of existing bonds and the formation of new ones. Synthesis of a complex molecule may involve a considerable number of individual reactions leading in sequence from available starting materials to the desired end product. Each step usually involves reaction at only one chemical bond in the molecule.
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In planning the route of chemical synthesis, chemists usually visualize the end product and work backward toward increasingly simpler compounds. For many compounds, it is possible to establish alternative synthetic routes. The ones actually used depend on many factors, such as cost and availability of starting materials, the amount of energy needed to make the reaction proceed at a satisfactory rate, and the cost of separating and purifying the end products. Moreover, knowledge of the reaction mechanism and the function of the chemical structure (or behaviour of the functional groups) helps to accurately determine the most-favoured pathway that leads to the desired reaction product.
A goal in planning a chemical synthesis is to find reactions that will affect only one part of the molecule, leaving other parts unchanged. Another goal is to produce high yields of the desired product in as short a time as possible. Often, reactions in a synthesis compete, reducing the yield of a desired product. Competition can also lead to the formation of side products which can be difficult to separate from the main one. In some industrial syntheses, by-product formation can be welcome if the by-products are commercially useful. Diethyl ether, for example, is a by-product of the large-scale synthesis of ethanol (ethyl alcohol) from ethylene. Both the alcohol and ether are valuable and can be separated easily.
The reactions involved in chemical syntheses usually, but not always, involve at least two different substances. Some molecules will change into others solely under the effect of heat, for example, while others react on exposure to radiation (e.g., ultraviolet light) or to electric current. However, where two or more different substances interact, they need to be brought into close proximity with one another. This is usually done by carrying out the syntheses with the elements or compounds in their liquid or gaseous states. Where the reactants are involatile solids, reaction is often carried out in solution.
The rate of a chemical reaction generally increases with temperature; chemical syntheses are thus often carried out at elevated temperatures. The industrial synthesis of nitric acid from ammonia and oxygen, for instance, is carried out at about 900 °C (1,650 °F). Frequently, heating will increase the rate of a reaction insufficiently or the instability of one or more reactants prevents application. In such cases catalysts—substances that speed up or slow down a reaction—are used. Most industrial processes involve the use of catalysts.
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Some substances react so rapidly and violently that only careful control of the conditions will lead to the desired product. When ethylene gas is synthesized to polyethylene, one of the most common plastics, a large amount of heat is released. If this release is not controlled in some way—e.g., by cooling the reactor vessel—the ethylene molecules decompose to carbon and hydrogen.
Many techniques have been developed to separate the products of chemical synthesis. These often involve a phase change. For example, the product of a synthetic reaction may not dissolve in a particular solvent, while the starting materials do. In this case, the product will precipitate out as a solid and can be separated from the mixture by filtration. Alternatively, if both starting materials and products are volatile, it may be possible to separate them by distillation.
Certain chemical syntheses lend themselves readily to the use of automated techniques. Automatic DNA (deoxyribonucleic acid) synthesizers, for example, are widely used to produce specific protein sequences.