Alcohols, a large class of organic compounds, are compounds in which hydrogen atoms in the side chains of aliphatic, alicyclic or aromatic hydrocarbons are replaced by hydroxyl groups.
Alcohol commonly referred to, it is a hydroxyl group with a saturated, SP3 hybrid of carbon atoms linked. If the hydroxyl group is connected to the benzene ring, it is phenol, if the hydroxyl group is connected to sp2 hybrid olefinic carbon, it is enol. Phenol and enol differ greatly from general alcohols.
Classification of Alcohol Names
According to the type of carbon atom to which the hydroxyl group is connected, it is divided into primary alcohol, secondary alcohol, and tertiary alcohol.
According to the type of hydroxyl group attached to the hydroxyl group, it is divided into fatty alcohol, alicyclic alcohol and aromatic alcohol. Fatty alcohols are classified into saturated alcohols and unsaturated alcohols based on whether the hydrocarbyl moiety contains an unsaturated bond.
The molecule contains a hydroxy different number, divided into monohydric alcohols, diols and triols and the like. Alcohols containing two or more hydroxyl groups are collectively referred to as polyols.
A hydroxyl group attached to the double bond carbon alcohols referred enol, enol generally unstable, isomerization stable carbonyl compound.
Customary nomenclature (Alcohol names)
Simple alcohols often adopt the customary naming method, that is, the word “alcohol” is added after the name of the hydrocarbon group connected to the hydroxyl group.
For example methanol, ethanol, propanol, etc.
More complex alcohols use systematic nomenclature.
The naming of saturated alcohols The longest carbon chain containing a hydroxyl group is selected as the main chain, numbered from the end closest to the hydroxyl group, and is called “some alcohol” according to the number of carbon atoms contained in the main chain.
Unsaturated alcohols named unsaturated alcohols are selected and the longest carbon chain hydroxyl-containing unsaturated bonds as the main chain, numbering from the end closest to the hydroxyl group. Referred to as “alcohol according to the number of carbon atoms in the main chain “Or” an alkynol “, the position of the hydroxyl group is represented by Arabic numerals, placed in front of the alcohol word.
The number representing the position of the unsaturated bond is placed in front of the olefinic or alkyne word so that the name of the parent is obtained, and then the name of the parent Name and position of the substituent.
The naming of polyhydric alcohols selects as many carbon chains as possible with -OH as the main chain. The number of hydroxyl groups is written in front of the alcohol word, and the order of the hydroxyl groups.
Alcohol compounds are affected by hydroxyl groups, and there are intermolecular hydrogen bonds. In water, there are also hydrogen bonds between alcohol molecules and water molecules. Therefore, their physical properties differ greatly from corresponding hydrocarbons. Mainly manifested in the relatively high melting point and a certain solubility in water.
Generally speaking, lower alcohols have better water solubility, and methanol, ethanol and propanol can be miscible with water in any ratio. Alcohols with 4 to 11 carbon atoms are oily liquids and are partially soluble in water.
Later, as the number of carbon atoms increases, the influence of hydrocarbon groups on molecules becomes greater and greater, and the physical properties of higher alcohols are closer to the corresponding hydrocarbons. In addition, lower alcohols have a special odor and spicy taste, while higher alcohols are odourless and tasteless.
Methanol (ligol) is produced from synthesis gas (CO and H₂) in the presence of heat, pressure and catalyst.
Ethanol, commonly known as alcohol, is the most widely used alcohol.
Glycol is the simplest and most important diol. It is a sticky, colorless liquid with a sweet taste.
Glycerol, commonly known as glycerin, is a colorless, viscous liquid with a sweet taste. It can be mixed with water, is insoluble in organic solvents, and has strong water absorption.
Industrial production of alcohol
In industrial production, with the exception of methanol, most of the commonly used simple saturated monohydric alcohols are produced from olefins, but before the rise of the petroleum industry, some alcohols were produced by fermentation.
The earliest method was methanol production by wood distillation, so methanol is also called wood alcohol. After 1920, this method was gradually stopped. Almost all methanol is produced by the catalytic conversion of synthesis gas—carbon monoxide and hydrogen—that is,
CO + 2H2 ——ZnO/Cr2O3, 400 ℃, 20 ～ 30MPa ——> CH3OH ΔH = -92KJ/mol
In the past 20 years, activated copper oxide has been used as a catalyst, and the reaction can be performed at 250 ° C and 5-10 MPa, which is more economical than the above conditions.
Fractional distillation of methanol from water can reach about 99% purity. To remove nearly 1% of the water, an appropriate amount of magnesium can be added. Methanol reacts with magnesium to form magnesium methoxide. It reacts with water to form insoluble magnesium oxide and methanol. After distillation, Obtained anhydrous methanol (more than 99.9%).
At present, the synthesis method is the most important method for preparing methanol.
The high-pressure process for the synthesis of methanol is the earliest and most widely used industrial methanol synthesis technology. The high-pressure process refers to a process for synthesizing methanol at a high temperature and pressure of 300 to 400°C and 30 to 35 MPa using a zinc-chromium catalyst. The raw materials are coal, water, and air. Hydrogen and carbon monoxide are obtained in the reaction of water and gas.
After dust removal, desulfurization, conversion, and water washing, they can be used to synthesize methanol. Catalyst ZnO, chromium trioxide, 300-400°C, 200-300 atmospheres, methanol vapor content reaches 10% at equilibrium.
After cooling, separation, crude methanol enters storage tanks, hydrogen and carbon monoxide can continue to be recycled. The purity of crude methanol is 80-93%. The main impurities are water, ethanol, dimethyl ether, and isobutanol, and purity can reach 99%.
Low-pressure method. ICl low-pressure method, Lurgi low-pressure method; low-pressure method has the economic advantage of low cost, the use of active copper catalysts to reduce the reaction temperature.
At present, the raw materials for the production of formazan have gradually shifted to oil and natural gas. The chemical network can mix methane and oxygen in a volume ratio of 9: 1 at the natural gas producing area, and pass through copper pipes at 200°C and 100 atmospheres. The reaction produced methanol.
Industrial methods for producing ethanol include grain fermentation, wood hydrolysis, sulfite, ethylene indirect hydration, ethylene direct hydration, acetaldehyde hydrogenation, carbon monoxide, and hydrogen carbonyl synthesis.
Among them, the ones that have industrial significance can be summarized into two major categories, namely, fermentation and ethylene hydration. Fermentation is a classic method of ethanol production, and it has been the main source of ethanol in many countries for a long time.
Today all the world’s drinking wine and 75% of industrial ethanol are still produced by fermentation. In the past 40 years, the trend of the fermentation method being replaced by ethylene water has become more and more obvious.
There are two methods in the ethylene hydration industry, one is indirect hydration with sulfuric acid as an absorbent; the other is direct hydration with ethylene catalysis.
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① The indirect hydration method is also called the sulfate method, and the reaction proceeds in two steps. First, ethylene is passed into concentrated sulfuric acid under a certain temperature and pressure conditions to generate sulfate esters, and then the sulfate esters are heated and hydrolyzed in a hydrolysis tower to obtain ethanol.
At the same time, a by-product ether is generated. Indirect hydration can use low-purity ethanol as raw material, with mild reaction conditions and high ethylene conversion, but the equipment is severely corroded and the production process is long. It has been replaced by direct hydration.
②Direct hydration Under certain conditions, ethylene reacts directly with water to produce ethanol through a solid acid catalyst:
In the other method, when adding water under the catalysis of olefin acid, phosphoric acid is used as a catalyst, and water vapor is passed into ethylene at 300°C. and 7 MPa pressure. It requires high concentration of ethylene and operates under high pressure. The production equipment is very demanding, and the amount of ethanol converted into it at one time is small. It must be recycled repeatedly and consume large energy.
The two methods mentioned above do not differ greatly in cost. Because ethylene can be obtained in large quantities from petroleum processing, it is valued by various countries.
The third method for producing ethanol is called the fermentation method.
After fermentation, starch-rich agricultural products such as cereals, potatoes, or wild plant fruits are washed and crushed, and then pressure-cooked to make the starch gelatinized, and then add a certain amount of water, cool to about 60°C and add amylase. The starch is sequentially hydrolyzed into maltose and glucose, and then yeast is added to ferment to obtain ethanol.
The industrial production of n-propanol is obtained by the reaction of ethylene, carbon monoxide and hydrogen under high pressure and heating using cobalt as a catalyst to obtain an aldehyde. This reaction is called oxo synthesis.
The aldehyde is further reduced to alcohol under the action of a catalyst. This is an extremely important method for the industrial production of aldehydes and alcohols.
The above method can also be used to produce higher aldehydes, but two isomers are often formed, and the aldehydes can be further reduced to alcohols.
The most important glycol is ethylene glycol, or 1,2-ethylene glycol, commonly known as glycol.
The industrial production method of ethylene glycol is prepared by ethylene oxide under pressure hydration or acid catalysis.
Pressurized hydration requires pressurized equipment and high temperature, but the post-treatment is convenient, so it is widely used; while acid-catalyzed hydration does not require pressure equipment and the reaction temperature is low, it is quite troublesome to remove sulfuric acid from the product.
The above two methods are used to produce ethylene glycol, and the total yield is more than 90% (based on ethylene oxide). At the same time, there are by-products diethylene glycol and tri ethylene glycol. The former can be used as a solvent for hydraulic braking. The working fluid of the equipment, the finishing and dyeing of fabrics, the latter can be used as solvents and plasticizers.
The most important triol is 1,2,3-propanetriol, commonly known as glycerol, which is formed by dripping glycerol into a mixed acid of concentrated nitric acid and concentrated sulfuric acid under strict cooling conditions.
The industrial production method of glycerol is chlorination of propylene at high temperature to obtain 3-chloropropene, which is then reacted with hypochlorous acid to obtain 1,3-dichloro-2-propanol and 2,3-dichloro-1-propanol. Under alkaline conditions, the mixture was cyclized to obtain 3-chloro-1,2-propylene oxide and then hydrolyzed to obtain glycerol.
Hydrolysis of haloalkanes
The corresponding alcohol can be obtained by performing a nucleophilic substitution reaction between a halogenated hydrocarbon and a dilute sodium hydroxide aqueous solution.
Halogenated hydrocarbons are prone to elimination reactions in NaOH alkaline solution. To avoid elimination reactions, silver hydroxide can be used instead of sodium hydroxide.
Reduction of carbonyl compounds
Aldehydes and ketones can be converted into alcohols by catalytic hydrogenation or under the action of reducing agents such as lithium aluminum hydride, sodium borohydride, diborane, aluminum isopropoxide, and active metals. Carboxylic acid derivatives can also form alcohols by catalytic hydrogenation or reduction with reducing agents such as lithium aluminum hydride, sodium borohydride, diborane, and active metals.