Experiment 4. Interaction of glycerin with copper (II) hydroxide
Reagents and materials: glycerin; copper sulfate, 0.2 N. solution; caustic soda, 2 N solution.
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Place 2 drops of copper sulfate solution and 2 drops of sodium hydroxide solution into a test tube and mix - a blue gelatinous precipitate of copper hydroxide (P) is formed. Add 1 drop of glycerin to the test tube and shake the contents. The precipitate dissolves and a dark blue color appears due to the formation of copper glycerate.
Process chemistry:
Glycerin is a trihydric alcohol. Its acidity is greater than that of monohydric alcohols: an increase in the number of hydroxyl groups enhances the acidic character.
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Glycerol easily forms glycerates with hydroxides heavy metals.
Moreover, its ability to form metal derivatives (glycerates) with multivalent metals is explained not so much by its increased acidity, but because in this case intra-complex compounds are formed that are particularly stable. Connections of this type are often called chelated(from the Greek ʼʼhelaʼʼ - claw).
Experiment 4. Interaction of glycerin with copper (II) hydroxide - concept and types. Classification and features of the category "Experiment 4. Interaction of glycerin with copper (II) hydroxide" 2017, 2018.
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DEFINITION
Glycerol It is a colorless, viscous, syrupy liquid with a sweet taste. Not poisonous. Glycerin is odorless.
Its melting and boiling points are 18 o C and 290 o C, respectively. Glycerin is hygroscopic and mixes well with water and ethanol. Absolutely pure anhydrous glycerin hardens at +18 o C, but it is extremely difficult to obtain it in solid form. The structure of the glycerol molecule is shown in Fig. 1.
Rice. 1. The structure of the glycerol molecule.
Glycerol is widely distributed in living nature. It plays an important role in metabolic processes in animal organisms, is part of most lipids - fats and other substances contained in animal and plant tissues and performing essential functions in living organisms.
Obtaining glycerin
The oldest method of producing glycerin is the hydrolysis of fats and oils:
Currently, glycerin is produced synthetically from propylene, which is formed during the cracking of petroleum. In this case, different ways of converting propylene into glycerol are used. The most promising method is the oxidation of propylene with atmospheric oxygen in the presence of a catalyst and at high temperature (kat = Cu, t 0 = 370). The process takes place in several stages.
Chemical properties of glycerin
Glycerol is a representative of trihydric alcohols, which, as hydroxyl-containing compounds, are characterized by the same reactions as monohydric alcohols.
Glycerol reacts with active metals(potassium, sodium, etc.), replacing hydrogen in all hydroxyl groups, react with hydrogen halides (HCl, HBr, etc.) in dehydration reactions, forming various esters.
Glycerin also has specific properties that distinguish it from monohydric alcohols: it reacts not only with alkali metals, but also with some bases, including insoluble ones, for example with copper (II) hydroxide:
The result of the reaction of glycerol with copper (II) hydroxide is copper glycerate (complex complex compound bright blue). This reaction is a qualitative reaction to polyhydric alcohols.
The most important in practical terms is the nitration reaction of glycerol, which results in the formation of trinitroglycerol C 3 H 5 (ONO 2) 3:
Application of glycerin
Glycerin is a component of many foods, creams and cosmetics.
Examples of problem solving
EXAMPLE 1
Place 2 drops of copper sulfate solution and 2 drops of sodium hydroxide solution into a test tube and mix - a blue gelatinous precipitate of copper (II) hydroxide is formed. Add 1 drop of glycerin to the test tube and shake the contents. The precipitate dissolves and a dark blue color appears due to the formation of copper glycerate.
Process chemistry:
Copper glycerate
Glycerin is a trihydric alcohol. Its acidity is greater than that of monohydric alcohols: an increase in the number of hydroxyl groups enhances the acidic character.
Glycerol easily forms glycerates with heavy metal hydroxides. However, its ability to form metal derivatives (glycerates) with multivalent metals is explained not so much by its increased acidity, but by the fact that this produces intra-complex compounds that are particularly stable. Compounds of this kind are called chelates (from the Greek “hela” - claw).
The reaction with copper hydroxide is a qualitative reaction to polyhydric alcohols and makes it possible to distinguish them from monohydric ones.
Oxidation ethyl alcohol copper oxide
Place 2 drops of ethyl alcohol into a dry test tube. Holding a copper wire spiral with tweezers, heat it in the flame of an alcohol lamp until a black coating of copper oxide appears. The still hot spiral is lowered into a test tube with ethyl alcohol. The black surface of the spiral immediately turns golden due to the reduction of copper oxide. In this case, the characteristic smell of acetaldehyde (the smell of apples) is felt.
The formation of acetaldehyde can be detected using a color reaction with fuchsulfurous acid. To do this, place 3 drops of fuchsinous acid solution in a test tube and add 1 drop of the resulting solution with a pipette. A pink-violet color appears. Write the equation for the oxidation reaction of alcohol.
Oxidation of alcohols with a chromium mixture
Place 2 drops of ethyl alcohol in a dry test tube, add 1 drop of sulfuric acid solution and 2 drops of potassium dichromate solution. The orange solution is heated over the flame of an alcohol lamp until the color begins to change to bluish-green. At the same time, the characteristic smell of acetaldehyde is felt.
Carry out a similar reaction using isoamyl alcohol or another alcohol available, noting the smell of the aldehyde formed.
Explain the chemistry of the process the chemistry of the process by writing the equations of the corresponding reactions .
Oxidation of ethyl alcohol with a solution of potassium permanganate
Place 2 drops of ethyl alcohol, 2 drops of potassium permanganate solution and 3 drops of sulfuric acid solution into a dry test tube. Carefully heat the contents of the test tube over the burner flame. The pink solution becomes discolored. There is a characteristic odor of acetaldehyde, which can also be detected by a color reaction with fuchsinsulfurous acid.
Chemistry of the process : (write the reaction equation).
Alcohols are oxidized more easily than the corresponding saturated hydrocarbons, which is explained by the influence of the hydroxy group present in their molecule. Primary alcohols are converted during oxidation into aldehydes under mild conditions, and into acids under more severe conditions. Secondary alcohols produce ketones upon oxidation.
