Organic oxygenated compounds, including various alcohols, are important functional derivatives of hydrocarbons. They are monoatomic, two - and polyatomic. Monohydric alcohols is, in fact, derivatives of hydrocarbons, in the molecular component of which one hydroxyl group (indicated by an "-OH") related to saturated carbon atoms.
Monohydric alcohols are widely distributed in nature. Thus, methyl alcohol in small amounts is contained in the juice of some plants (e.g. Hogweed). Ethyl alcohol, as a product of alcoholic fermentation of organic compounds contained in podkosa fruits and berries. Cetyl alcohol was found in the whale's fat. Beeswax includes ceremony, kirillovyh alcohols. Rose petals discovered 2-phenylethanol. Terpene alcohols in the form of scented compounds present in many spices and aromatic crops.
Alcohols are classified by the molecular number of hydroxyl groups. Primarily on:
- Monohydric alcohols (e.g., ethanol)
- diatomic (ethanediol)
- polyhydric (glycerol).
The nature of the hydrocarbon radical, alcohols are divided into aromatic, aliphatic, cyclic. Depending on the type of carbon atom connected with a hydroxyl group, alcohols are considered as primary, secondary and tertiary. The General formula of Monohydric alcohol in use to the limit of monatomic alcohols is expressed by the value: n H2n +2O.
The name of the spirits, by radical-functional nomenclature formed from the name associated with a hydroxyl group radical, and the words "alcohol". For the systematic nomenclature IUPAC name of the alcohol formed from the corresponding alkanes with the addition of the ending "-ol". For example:
- methanol – methyl alcohol
- methylpropanol-1-2 – isobutyl (tert-butyl)
- ethanol – ethyl
- butanol-1-2 – butyl (verboselevel)
- propanol-1-2 – propyl (izopropilovyi).
Numbering according to IUPAC rules, classified by the position of the hydroxyl group, it receives a smaller number. Example: pentanediol-2-4, 4-pentanol-2, etc.
Limiting Monohydric alcohols have the following types of structural and spatial isomerism. For example:
- The carbon skeleton.
- Simple isomeric esters.
- Position of the functional group.
The spatial isomerism of the alcohols represented by the optical isomers. Optical isomerism is possible in the presence in the molecule of asymmetric carbon atom (containing four different Deputy).
The methods of producing Monohydric alcohols
To limit Monohydric alcohol in several ways:
- Hydrolysis halogenoalkanes.
- The hydration of alkenes.
- Recovery of aldehydes and ketones.
- Magnetogenesis synthesis.
Hydrolysis halogenoalkanes is one of the most common laboratory methods of receiving of alcohols. Processing of water (as an alternative aqueous alkali solution) alcohols receive primary and secondary:
Tertiary halogenoalkane hydrolyzed even easier, but they are easier it is a side reaction of elimination. Therefore, tertiary alcohols get by other methods.
Hydration of alkenes is joining alkaram water in the presence of acidic catalysts (H3 PO4). The method is the basis for the industrial production of such alcohols as ethyl, isopropyl, tert-butyl.
Recovery of the carbonyl group is carried out with hydrogen in presence of hydrogenation catalyst (Ni or Pt). From ketones with the formation of secondary alcohols from aldehydes – limit of primary Monohydric alcohols. Formula process:
Joining the aldehydes and ketones alkalinisation get magnesium-organic compounds. The reaction is carried out in dry diethyl ether. Subsequent hydrolysis magyarkanizsa compounds forms a monoatomic alcohols.
Primary alcohols are formed by the Grignard reaction of formaldehyde only and any alkalinisation. Other aldehydes give this reaction a secondary alcohol ketone tertiary alcohols.
Industrial synthesis of methanol
Industrial methods usually are continuous processes where multiple recycling of large masses of the reacting substances, carried out in the gas phase. Commercially important alcohols are methanol and ethanol.
Methanol (its production volume is the biggest among alcohols) until 1923, received dry distillation (heating without access of air) of wood. Today it is generated from synthesis gas (mixture of CO and H2 ). The process is carried out under a pressure of 5-10 MPa with the use of oxide catalysts (ZnO Cr2 O3. CuO ZnO Al2 O3 and others) in the temperature range 250-400C, received as a result of the limiting Monohydric alcohols. The formula of the reaction: CO 2H2 → CH3OH.
In 80-e years in the study of the mechanism of this process it was found that methanol is not formed from carbon monoxide and carbon dioxide, resulting in the interaction of carbon monoxide with traces of water.
Industrial synthesis of ethanol
Common industrial method of synthesis of technical ethanol is hydration of ethylene. Formula Monohydric alcohol of ethanol will receive the following:
The process is carried out under a pressure of 6-7 MPa in the gas phase, flowing the ethylene and water vapor over the catalyst. Catalyst are phosphoric or sulfuric acid deposited on silica gel.
Food and medical ethyl alcohol is obtained by enzymatic hydrolysis of the sugars contained in grapes, berries, cereals, potatoes with subsequent fermentation of the resulting glucose. Fermentation of sugary substances called yeast fungi belonging to the group of enzymes. To process the most favorable temperature of 25-30C. Industrial enterprises used ethanol, obtained by fermentation produced by the hydrolysis of wood waste and pulp and paper production of carbohydrates.
Physical properties of Monohydric alcohols
Alcohol molecules are the hydrogen atoms connected with the electronegative element of oxygen, virtually devoid of electrons. Between these hydrogen atoms and oxygen atoms having unshared pairs of electrons, the formation of intermolecular hydrogen bonds.
Hydrogen bond due to the specific features of the hydrogen atom:
- When pulling the bonding electrons to the more electronegative atom - the hydrogen atom "laid bare", and formed other electrons unshielded proton. During ionization of any other atom is still electron shell, shielding the nucleus.
- The hydrogen atom has a small size compared to other atoms, so that it is able to penetrate deep enough into the electron shells of neighboring negatively polarized atom not being connected with it by a covalent bond.
Hydrogen bonds are about 10 times weaker than ordinary covalent. The energy of hydrogen bonds is in the range of 4-60 kJ/mol, of the alcohol molecules it is 25 kJ/mol. From the usual s-links and it differs in the greater length (0,166 nm) compared to the length of the link O-H (0,107 nm).
The chemical reaction of Monohydric alcohols are determined by the presence in their molecules of hydroxyl groups that are functional. The oxygen atom is in sp3-hybrid state. The bond angle close to tetrahedral. Two sp3-hybrid orbitals go to the formation of bonds with other atoms, and the other two orbitals are the lone pairs of electrons. Accordingly, the oxygen atom centered partial negative charge and the hydrogen atoms and carbon atoms partial positive charges.
The C-O and C-H covalent polar (the latter is more polar). Generalities the communication gap O-H education H determines the acidic properties of Monohydric alcohols. A carbon atom with a partial positive charge can be the object of attack of the nucleophilic reagent.
Alcohols are very weak acids, weaker than water but stronger than acetylene. They do not cause discoloration of the indicator. The oxidation of Monohydric alcohols is manifested in the interaction with the active metals (alkaline and alkaline-earth) with evolution of hydrogen and formation of ALCOHOLATES:
2ROH 2Na → H 2RONa2.
ALCOHOLATES of alkali metals – substances with ionic bonds between oxygen and sodium, in a solution of Monohydric alcohol they dissociate with the formation of altosid ions:
CH3 ONa → CH3 O – Na (device methoxide ion).
The formation of ALCOHOLATES may also be carried out by reaction of the alcohol with sodium amide:
And will there be a reaction of the ethanol with alkali? Virtually no. Water is a stronger acid than ethyl alcohol, so there is an equilibrium. With increasing length of the hydrocarbon radical in the alcohol molecule acidic properties are reduced. Also, limiting Monohydric alcohols are characterized by a decrease of acidity in the series: primary → secondary → tertiary.
The reaction of nucleophilic substitution
In alcohols the bond C-O is polarized, the carbon atom is concentrated partial positive charge. As a consequence, the carbon atom attacked by the nucleophilic particles. In the process of breaking the C-O and a substitution of another nucleophile hydroxyl group.
One of such reactions is the interaction of alcohols with galogensoderjasimi or their concentrated solutions. Reaction equation:
To facilitate cleavage of the hydroxyl group is used as a catalyst concentrated sulfuric acid. She profaniruet an oxygen atom, thereby activating the molecule of a Monohydric alcohol.
Primary alcohols, and primary halogenoalkane, enter into exchange reaction mechanism SN2. Secondary Monohydric alcohols, as secondary halogenoalkane react with hydrohalic acids. Interaction terms between alcohol are subject to the nature of the reacting components. Reactivity of alcohols obeys the following laws:
Under mild conditions (neutral or alkaline solutions of potassium permanganate, chromic mixture at a temperature of 40-50°C) to oxidize primary alcohols to aldehydes, when heated to higher temperatures – up to acids. Secondary alcohols are oxidized to ketones. Tertiary oxidized in the presence of acid in very harsh conditions (e.g. chrome mixture at a temperature of 180°C). The oxidation reaction of the tertiary alcohol goes through dehydration of the alcohol with the formation of the alkene and oxidation of the latter with rupture of the double bond.