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Butlerov and his theory of chemical

HYDROCARBONS

Hydrocarbons are compounds of hydrogen and carbon. They may be gaseous, liquid or solid. They are found in nature or synthesized. Hydrocarbons may possess widely different chemical reactivities. Some of them are toxic, some are explosive. Hydrocarbons and their derivatives cover the whole domain of organic chemistry and form the basis of plant and animal life. The most prolific sources of hydrocarbons are petroleum and coal (for the non-aromatic and aromatic hydrocarbons). Saps and vegetable juices are sources of terpenes.

The number of hydrocabons theoretically possible is infinite. A paraffin hydrocarbon having 20 carbon and 42 hydrogen atoms in a molecule may have over 350,000 different combinations of these atoms which are known as isomers. This number is small in comparison with the numbers of possible isomers for other than paraffin hydrocarbons. Even if some isomers are thermodynamically unstable, the number of hydrocarbons that may yet be discovered is amazing.

The number of hydrocarbons metioned in the literature exceeds one hundred thousand; few of them have been investigated.

Simplifications are necessary for studying the vast field of the chemistry of hydrocarbons. Several classification systems were developed to assist in these studies.

The statistical system assembles hydrocarbons in groups which differ from each other by two hydrogen atoms present in the molecules containing an equal number of carbon atoms.

The structural (chemical) system finds the widest recognition. It classifies hydrocarbons by the series which reflect the physical and chemical properties of their members in structural similarities.

QUESTIONS

1. What are hydrocarbons?

2. In what state may hydrocarbons occur?

3. Which are the most prolific sources of hydrocarbons?

4. Is the number of hydrocarbons theoretically possible large or small?

5. What is the number of hydrocarbons mentioned in literature?

6. What systems were developed in the studies of hydrocarbons?

7. W7hat system finds the widest recognition?

8. How does this system classify hydrocarbons?

 

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ISOMERIZATION

When chemical substances have the same molecular formula and molecular weight but different properties, they are called isomers (of each other) and the reaction of transformation of one isomer into another is called isomerization.

The reason for this phenomenon lies in the difference in configuration of atoms in the molecule.

There are, for example, two different compounds with the chemical formula C4H10:

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n-butane iso-butane

These compounds have different properties.

Isomerisrn is prevalent among more complex compounds. Thus glucose is one of 16 isomeric sugars of the composition C6H12O6.

QUESTIONS

1. What substances are called isomers?

2. What do you call the reaction of transformation of one isomer into another?

3. What is the reason for isomerizat ion?

4. Have n-butane and iso-butane equal or different properties?

5. What is the formula for glucose?

 

 

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BUTLEROV AND HIS THEORY OF CHEMICAL

STRUCTURE

A. M. Butlerov was born in 1828 in the town of Chistopol. In 1849 he graduated from the Kazan University, where he studied under the prominent Russian chemists K. Klaus and N. Zinin. After graduation Butlerov was left at the University and soon he began to deliver lectures in chemistry. For his prominent scientific merits Butlerov was elected a full member of the Russian Academy of Sciences.

From the very first steps of his scientific activities Butlerov showed himself to be a brilliant experimentor and carried out a number of remarkable syntheses.

Butlerov put forth a number of profound and daring ideas in the field of theoretical chemistry.

The essence of Butlerov's theory consists in the statement that the properties of substances depend not only on their qualitative and quantitative composition, as was thought previously, but on their internal molecular structure as well, and on how the atoms, making up the molecule, are linked with each other. Butlerov called this internal arrangement "chemical structure". Butlerov's theory of chemical structure of molecules is the theoretical foundation of organic chemistry.

QUESTIONS

1. When was A. M. Butlerov born?

2. Where did Butlerov receive his education?

3. Where did Butlerov work after graduation from the University?

4. What does the essence of Butlerov's theory consist in?

5. What did Butlerov call the internal arrangement of atoms?

6. What is the theoretical foundation of Butlerov's theory?

 

 

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ACETYLENE

Acetylene is a colourless gas, the first and the only commercially important member of the family of aliphatic hydrocarbons which contain a triple bond. It has the formula CH= =CH. It is made cheaply by adding water to calcium carbide:

CaC2 + 2H2O > CH EESSE CH + Ca(OH)2

Calcium Two molecu- Acetylene Calcium

carbide les of water hydroxide

Other methods are also used. Liquid acetylene is unstable to shock, but can be handled safely in tanks containing porous material saturated with acetone.

Acetylene is used mostly as a chemical intermediate and for oxyacetylene welding of metals. The temperature of the oxyacetylene flame is 2,800 C.

QUESTIONS

1. What kind of gas is acetylene?

2. What is the formula for acetylene?

3. How is acetylene produced?

4. In what way can liquid acetylene be handled safely?

5. Where is acetylene mostly used?

6. What is the temperature of the oxyacetylene flame?

 

 

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RUBBER

Natural rubber is an elastic substance found as milky dispersion in many species of plants. Synthetic rubbers are high polymeric elastic substances manufactured from a wide range of chemical compounds. Both synthetic and natural rubber have in common the ability to undergo nearly reversible, highly elastic deformations.

In 1960 world-wide use of rubber was divided nearly equally between natural product (about 2 million long tons) and synthetic rubber (about 1.8 million long tons).

Natural rubber is closely related chemically to many other naturally occurring compounds, from animals as well as plants, including terpenes and steroids. These are known collectively as isophenoids. The basic building block for natural rubber as well as other polyisophenoids is acetic acid.

Natural rubber occurs in a separate system of latex vessels just under the outer bark. Latex is collected, bulked and coagulated. Rubber was first obtained from wild trees in Brazil.

The physical and chemical properties of natural rubber are fixed by biological factors. In synthetic rubber a much greater variation of properties can be realized. However, in both natural and synthetic rubber the properties are resultant contributions of the fine structures and of the gross molecules of the polymer. The chemical properties of rubber are of paramount importance.

QUESTIONS

1. What is natural rubber?

2. What are synthetic rubbers manufactured from?

3. What is the main property of both natural and synthetic rubber?

4. Where does natural rubber occur?

5. In what country was natural rubber first obtained?

6. What are the physical and chemical properties of natural

rubber fixed by?

 

 

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VULCANIZATION

Vulcanization is a process used to make raw rubber useful; it decreases sensitivity to extremes of temperature, confers resistance to flow under stress, and stabilizes rubber's valuable properties, e. g. abrasion resistance, resilience, and impermeability to fluids. Chemically, vulcanization creates strong bonds between the long linear molecules of the rubbery polymer, efficiently fixing the molecules' position with respect to one another, and preventing their slippage under stress. Solid rubber is prepared for vulcanization by a process known as compounding, i. e. mixing with other ingredients in internal mixers which uniformly blend the rubber and the added ingredients. Sulphur is the most used vulcanizing agent. Other materials commonly added before vulcanization include: accelerators to speed vulcanization, zinc oxide and fatty acid to improve properties, carbon black or other fillers to strengthen the final product, and anti-oxidants to protect against effects of light, heat, and oxygen. The fully compounded rubber is extruded or calendered (depending on the properties wanted) to the final form, and then vulcanized. This usually is done in a mould with the aid of heat, although some mixtures permit cure at room temperature.

Vulcanizing agents besides sulphur are often used, particularly for some heat and solvent resistant rubbers, including peroxides, modified phenols and metallic oxides. Some types of rubber have been vulcanized experimentally by high energy radiation.

QUESTIONS

1. What is vulcanization?

2. What does vulcanization create?

3. By what process is solid rubber prepared for vulcanization?

4. What is compounding?

5. Which is the most used vulcanizing agent?

6. What other materials are commonly added before vulcanization?

7. How is the fully compounded rubber processed?

8. By what method have some types of rubber been experimentally vulcanized?

 

 

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NATURAL GAS

Natural gas is an inflammable gas that occurs in the earth's crust and is found with or near accumulations of crude oil. Being in gaseous form, it may occur alone in separate reservoirs.

Typical natural gas consists of hydrocarbons having a very low boiling point. Methane (CH4), the fundamental member of the methane series, with a boiling point of254 F, makes up approximately 85 per cent of the typical gas. Ethane (C2He), with a boiling point of 128 F, is present in amounts up to 10%, and propane (CSH8), with a boiling point of 44 F, up to 3%. Butane (C4H10), pentane (C5H12), hexane and octane may be present.

Nearly all natural gas is inflammable. It has no distinct odour. Its main use is for fuel, but it is also used to make carbon black, natural gasoline, liquefied petroleum gas, and certain chemicals.

A method has been perfected to change methane into liquid form.

 

QUESTIONS

1. What is natural gas?

2. Where does natural gas occur?

3. What does typical natural gas consist of?

4. Which is the fundamental member of the methane series?

5. What is the boiling point of ethane?

6. What is the main use of natural gas?

7. Are there any methods of changing methane into liquid form?

 

 

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PETROLEUM

Petroleum is a complex mixture of hydrocarbons. It contains small amounts of oxygen, nitrogen, and sulphur compounds, and traces of metal salts. Hundreds of compounds of varying composition, molecular weight, and structure have been identified. Their properties are extremely varied: some boil below room temperature, some cannot be distilled without decomposition; all are combustible. Many special products come from petroleum: lubricants, waxes, solvents, asphalts for roads, medicinal oils, and numberless chemical derivatives. But the tremendous growth of the petroleum industry has been based on demand for fuels: gasoline, diesel oil, house heating oils, and heavy fuel oils for industrial furnaces and steam and power generation.

QUESTIONS

1. What kind of mixture is petroleum?

2. What compounds does petroleum contain?

3. What are the special products corning from petroleum?

4. What has the tremendous growth of the petroleum industry been based on?

 

 

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PETROLEUM PROCESSING

The petroleum refining industry is one of the largest manufacturing industries.

Crude oil is a mixture of many different hydrocarbon compounds, making the chemistry of petroleum refining extremely complex. The refining processes can be grouped under three main headings: (1) separating the crude oils to recover the desired products; (2) breaking the remaining large chemical compounds into smaller chemical compounds by cracking; (3) building the desired chemical compounds by chemical reactions, such as polymerization, reforming, isomeri-zation, etc.

Refinery products, such as gasoline, kerosine, diesel oil, and others, are not pure chemical compounds but mixtures of chemical compounds.

QUESTIONS

1. What industry is one of the largest manufacturing industries?

2. What does crude oil consist of?

3. Under what main headings can the refining process be grouped?

4. Are these products pure chemical compounds or mixtures of chemical compounds?

 

 

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CRACKING

The major product from the refinery is the motor fuel (gasoline). Of course kerosine, diesel oil, jet fuels (mostly kerosine fraction), and others are extremely important also. On the average the fraction of gasoline is not over 20% of the total volume of crude oil. If more gasoline than 20 pel cent obtainable by distillation is desired, it is necessary to resort to other means than straight separation to get more gasoline. This can be done either by recombining the gaseous, or lighter, molecules (polymerization), or by breaking down the heavier molecules (cracking). The cracking may be done either by thermal means (maintaining the heavy fractions at high temperatures), or by catalytic means.

In catalytic cracking the fraction to be cracked is contacted with a catalyst under lower pressure conditions than in thermal cracking. Catalytic cracking gives much better yields of gasoline, low carbon formation, and a gasoline of much higher octane number.

QUESTIONS

1. What is the major product from the refinery?

2. What other products are obtained from the refinery?

3. How much gasoline does crude oil usually contain?

4. By what methods can more gasoline be obtained?

5. What is cracking?

6. By what means can cracking be done?

 

 

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ALCOHOLS

Alcohols are classified as monohydric, dihydric, tri-hydric, etc., according to the number of hydroxyl groups they contain.

Alcohols in general are colourless liquids or solids. The simpler monohydric alcohols are liquids, and viscosity increases with molecular weight. Polyhydric alcohols are syrupy liquids. Alcohols with more complex formulas are generally solids. In general, water solubility decreases as the formula becomes more complex. Boiling points increase as the straight-chain alcohols become more complex. The alcohol may be dehydrated or the hydrogen of the hydroxyl group replaced by a metal. Alcohol will form esters with an organic acid by the elimination of water.

Methyl alcohol (wood alcohol) is produced by destructive distillation of wood or by synthesis under pressure of hydrogen and carbon monoxide.

The pure product is completely miscible with water and is a solvent for fats, oils, resins and nitro-cellulose. It is widely usedformethylationof organic compounds, particularly dyestuffs. It is the raw material for making formaldehyde and an intermediate in synthesis of phenolic and other resins. It is used in antifreeze solutions and in special fuels.

QUESTIONS

1. How are alcohols classified?

2. What are the properties of alcohols?

3. What does the viscosity of alcohols increase with?

4. May alcohols be dehydrated?

5. How is methyl alcohol produced?

6. What are the properties of methyl alcohol?

7. Where is methyl alcohol used?

 

 

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