most famous and used in human life and industrial substances belonging to the category of polyols - is ethylene glycol and glycerol.Their study and use began several centuries ago, but the properties of these organic compounds in many ways unique and unique that makes them indispensable to this day.The polyols used in many chemical syntheses, industries and spheres of human activity.
first "acquaintance" with ethylene glycol and glycerol history producing
In 1859, through a two-stage process of interaction dibromoethane with silver acetate and subsequent treatment with potassium hydroxide produced in the first reaction of ethylene glycol, Charles Wurtz first synthesized ethylene glycol.Some time later the method was developed for the direct hydrolysis dibromoethane, but on an industrial scale in the early twentieth century dihydric alcohol 1,2-dihydroxyethane, it - monoethylene glycol, or a glycol, in the United States was obtained by hydrolysis of ethylene.
Today and in the industry and in the laboratory used a number of other methods, new, more economical with raw materials and energy point of view, and environmentally friendly as well as the use of reagents containing or releasing chlorine, toxins, carcinogens and other hazardousenvironment and human substance is reduced with the development of "green" chemistry.
Aptekar Carl Wilhelm Scheele in 1779 opened glycerol, and especially the composition of the compound studied in 1836 Theophile Jules Pelouse.Two decades later it was found out and grounded triatomic molecular structure of alcohol in the writings of Pierre Eugene Berthelot Marseleya and Charles Wurtz.Finally, even twenty years after Charles Friedel had a total synthesis of glycerol.Currently, industry uses two methods for its preparation: through allyl chloride from propylene via acrolein as well.Chemical properties etilengilikolya as glycerin is widely used in various fields of chemical industry.
Structure and structure of the compound
At the heart of the molecule is unsaturated hydrocarbon skeleton of ethylene, consisting of two carbon atoms, in which there was a gap of a double bond.On the vacated space at the valence of carbon atoms joined by two hydroxyl groups.Formula ethylene - C2H4, after rupture faucet connection and attachment of the hydroxyl groups (a few steps), it looks like C2H4 (OH) 2.That is ethylene glycol.
ethylene molecules characterized by a linear structure, while the dihydric alcohol is a kind of trans-konfigurtsii in the placement of hydroxyl groups with respect to the carbon skeleton and to each other (as the term is fully applicable to the situation with respect to the double bond).Such dislocation corresponds to the remote location of the hydrogens of the functional groups, less energy, and therefore - the maximum stability of the system.Simply put, one OH-group "looks" up, and the other - down.At the same time are unstable compound with two hydroxyl groups: with one carbon atom to form a reaction mixture, they immediately dehydrate passing into aldehydes.
chemical properties of ethylene glycol is determined by its origin from the group of polyols, namely subgroups diol, ie compounds with two hydroxyl moieties on adjacent carbon atoms.Substance, also contain several OH-substituent is and glycerol.It has three functional groups and alcohol is the most common representative of its subclass.
Many of the compounds in this class are also prepared and used in the chemical industry for various syntheses and other purposes, but the use of ethylene glycol has a more serious scale, and is involved in virtually all industries.This will be discussed in more detail below.
Application of ethylene due to the presence of a number of properties that are inherent in a polyhydric alcohol.This distinctive features that are unique to this class of organic compounds.
most important of the properties - is unlimited ability to mix with H2O.Water + glycol gives a solution with a unique feature: the temperature of its freezing point, depending on the concentration of the diol below 70 degrees, than the pure distillate.It is important to note that this dependence is nonlinear, and reaches a certain quantitative glycol begins opposite effect - the temperature of freezing increases with the percentage of solute.This feature has been applied in the production of various antifreeze liquids "nezamerzaek" which crystallize at extremely low thermal characteristics of the environment.
Except in water, the dissolution process proceeds well in alcohol and acetone, but not observed in paraffin, benzene, ether and carbon tetrachloride.Unlike its ancestor aliphatic - a gaseous substance such as ethylene glycol, ethylene glycol - a syrupy, clear, with a slight tinge of yellow liquid, sweetish taste, with uncharacteristic smell is almost non-volatile.Freezing occurs at one hundred percent of ethylene glycol - 12.6 degrees Celsius, and boiling - at 197.8.Under normal conditions, the density is 1.11 g / cm3.
Methods for producing ethylene glycol can be obtained in several ways, some of them today have only historical or preparative value, and others are actively used by a person on an industrial scale, and not only.Following in chronological order, let us consider the most important.
have already been described by the first method of producing ethylene dibromoethane.Formula ethylene double bond is broken, and the free valence are occupied by halogens, - the main starting material in this reaction - in addition to carbon and hydrogen in its structure has two bromine atoms.The formation of the intermediate compound in the first stage of the process is possible just because of their cleavage, ie. E. Replacement of acetate groups, which upon further hydrolysis converted into alcohol.
During further development of science has become possible to produce ethylene by direct hydrolysis of any ethanes substituted with two halogens on adjacent carbon atoms, by aqueous solutions of alkali metal carbonates or the group (less environmentally reagent) H2O and lead dioxide.The reaction is quite "time consuming" and occurs only at much higher temperatures and pressures, but that did not stop the Germans during the world wars to use this method for the production of ethylene in an industrial scale.
a role in the development of organic chemistry has played a method of production of ethylene glycol from coal by hydrolysis alkali metal salts of the group.By increasing the reaction temperature to 170 degrees the yield reached 90%.But there was a significant drawback - glycol had somehow removed from the salt solution, which is directly associated with a number of difficulties.The researchers solved this problem by developing a method with the same starting material, but by breaking the process into two stages.
etilenglikolatsetatov Hydrolysis, as the final stage of the method previously Wurtz, became a separate way, when managed to get a starting material by oxidation of ethylene in acetic acid with oxygen, that is, without the use of expensive and not harmless at all halogen compounds.
also known many methods of production of ethylene glycol by oxidation hydroperoxides, peroxides, organic peracids in the presence of catalysts (osmium compounds), potassium chlorate, and others. There are also electro-chemical and radiation methods.
Characteristics common chemical properties
chemical properties of ethylene glycol is determined by its functional groups.The reactions may be involved one hydroxyl substituent or both, depending on the process conditions.The main difference in reactivity is that due to the presence in the polyhydric alcohol hydroxyl number and their mutual influence is stronger acidic properties than monovalent "peers."Therefore, reactions with alkali products are salt (glycol - glycolates for glycerol - glycerate).
The chemical properties of ethylene glycol as well as glycerol, the reaction includes all categories of monohydric alcohols.Glycol gives complete and partial esters in reactions with monobasic acids, glycolates, respectively, are formed with alkali metals and with a chemical process with strong acids or salts thereof released aldehyde acetic acid - due to cleavage of molecules of the hydrogen atom.
Reacts with active metals
reaction of ethylene glycol with active metals (standing after the hydrogen in the chemical series tension) at elevated temperatures gives an ethylene glycol metal plus hydrogen is released.
C2H4 (OH) 2 + H → S2N4O2H, where X - the active divalent metal.
Qualitative reaction to ethylene
polyol distinguish from any other liquid you can use the visual reactions peculiar to this class of compounds.To this end, colorless solution was poured alcohol-precipitated hydroxide of copper (2) having a characteristic blue color.The interaction of the mixed components is observed and the dissolution of the precipitate in the saturated solution staining blue color - due to the formation of copper glycolate (2).
chemical properties of ethylene glycol are important for the production of solvents.Intermolecular dehydration of the substance, that is the elimination of water from each of two molecules of glycol and their subsequent association (one hydroxyl group is split off completely, and from other waste only hydrogen), makes it possible to obtain a unique organic solvent - dioxane, which is frequently used in organic chemistry,in spite of its high toxicity.
Exchange hydroxyl by halogen
In the reaction of ethylene glycol with hydrohalic acids observed replacing the hydroxyl groups of the respective halogen.The degree of substitution depends on the molar concentration of hydrogen halide in the reaction mixture:
HO-CH2-CH2-OH + X → 2NH-CH2-CH2-X, where X - chloro or bromo.Preparation of esters
In reactions of ethylene with nitric acid (specific concentration) and monobasic organic acids (formic, acetic, propionic, carnival, valeric and t. D.) The formation of the complex and, accordingly, monoethers.With other concentrations of nitric acid - di- and trinitroefirov glycol.As the catalyst, sulfuric acid is used a predetermined concentration.
Critical glycol derivatives
valuable substances, which are obtainable from polyhydric alcohols by simple chemical reactions (as described above), are ethers of ethylene glycol.Namely monomethyl and monoethyl whose formulas - HO-CH2-CH2-O-CH3 and HO-CH2-CH2-O-C2H5, respectively.Chemical properties, they are a lot like glycols, but, just like any other class of compounds have unique reaction characteristics that are unique to them:
- Monometiletilenglikol is a liquid without color, but with a characteristic disgusting odor, boils at 124, 6 degrees Celsius, well dissolved in ethanol and other organic solvents and water are significantly more volatile than the glycol, and a density less than that of water (about 0.965 g / cm3).
- Dimetiletilenglikol - as a liquid, but less characteristic odor, density of 0.935 g / cm3, the temperature of boiling 134 degrees above zero and the solubility, relative to the previous homologue.
Application cellosolve - in general, so called mono ethylene glycol - is quite common.They are used as reactants and solvents in organic synthesis.Also apply to their physical properties and anti-corrosion additives in anticrystallization antifreeze and motor oil.
Applications and pricing of a production series
cost factories and enterprises engaged in the production and sale of such chemicals, ranges from an average of about 100 rubles per kilogram of such chemical compounds as ethylene glycol.The price depends on the purity of the substance and the maximum percentage of the desired product.
The use of ethylene glycol is not limited to any one area.Thus, in its use as a raw material in the production of organic solvents and synthetic resin fibers, liquid, freezing at low temperatures.He is involved in many industries such as automotive, aviation, pharmaceutical, electrical, leather, tobacco.Let's face it the weight of its importance for organic synthesis.
important to remember that the glycol - a toxic compound that can cause irreparable damage to human health.Therefore, it is stored in sealed containers made of aluminum or steel with optional inner layer protects the tank from corrosion, in an upright position, and rooms are not equipped with heating systems, but with good ventilation.Period - no more than five years.