Organic Chemistry

Reactivity order of Alcohols

Chemical properties of Alcohols

There are two pairs of orphaned electrons on the oxygen of the alcoholic hydroxyl group, and the oxygen can be combined with the proton by the lone pair of electrons. Reactivity order of alcohols

Acidity and alkalinity of alcohol

Therefore, alcohol is alkaline. In the alcoholic hydroxyl group, since the electronegativity of oxygen greater than hydrogen electronegativity, oxygen, and hydrogen, and therefore shared electrons tend to oxygen, hydrogen showed some activity, it also has acidic alcohol.

The acidity and basicity of the alcohol are related to the electronic effect of the hydrocarbon group attached to the oxygen. The stronger the electron-withdrawing ability of the hydrocarbon group, the weaker the alkalinity of the alcohol and the stronger the acidity.

Reactivity order of alcohols

On the contrary, the stronger the electron donating ability of the hydrocarbon group, the stronger the alkalinity of the alcohol and the weaker the acidity. Reactivity order of alcohols

The steric hindrance of the hydrocarbon group also has an effect on the acidity and alkalinity of the alcohol, so it is important to analyze the electronic effect and steric hindrance of the hydrocarbon group.

Hydrogen reaction in alcoholic hydroxyl groups

Since the hydrogen in the alcoholic hydroxyl group has a certain activity, the alcohol can react with the sodium metal, the hydrogen-oxygen bond is broken, and sodium alkoxide is formed and hydrogen gas is evolved.

Since water is more acidic than alcohol in the liquid phase, the reaction of an alcohol with sodium metal is not as strong as the reaction of water and sodium metal. Reactivity order of alcohols

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If sodium alkoxide is placed in water, the sodium alkoxide will be completely hydrolyzed to form alcohol and sodium hydroxide. Nonetheless, industrial sodium or sodium ethoxide is still reacted with alcohol and sodium hydroxide, and then the water is removed to balance the sodium alkoxide.

A common method is to use an azeotropic mixture to carry the water away from equilibrium. The boiling mixture refers to several liquid mixtures which have different boiling points and are completely mutually soluble.

Due to the intermolecular forces, they cannot be separated due to the same composition of the gas phase and the liquid phase during the distillation process, and the lowest boiling point is obtained (all groups).

A distillate having a low boiling point or a highest boiling point (higher than the boiling point of all components). The composition of these distillates is the same as the composition of the solution until the boiling point is constant.

Such as ethanol-benzene-water to form a ternary azeotrope, the boiling point of which is 64.9 ° C (ethanol 18.5%, benzene 74%, water 7.5 %), a benzene-ethanol consisting of a binary azeotrope having a boiling point of 68.3 ° C (ethanol 32.4%, benzene 67.6%). Reactivity order of alcohols

Since ethanol-water forms an azeotropic mixture, its boiling point is 78 ° C (95.57% ethanol, 4. 43% water), so a small amount of water in ethanol cannot be removed by distillation, and the ratio of addition can be calculated to form ethanol-benzene-water.

A slight excess of benzene in the ternary azeotrope is first removed by water, and then excess benzene is formed into a binary azeotrope with ethanol, leaving anhydrous ethanol.

An alcohol solution of sodium alkoxide can be obtained by the above-described dehydration method. Sodium alkoxide and its analogs are an important class of agents in organic synthesis and are often used as bases.

The reaction of an Alcohol with an oxygenated inorganic acid

The alcohol reacts with the oxy-inorganic acid to lose one molecule of water to form an inorganic acid ester.

The reaction process of alcohol and nitric acid is as follows: the alcohol molecule acts as a nucleophile to attack the positively charged portion of the acid or its derivative, the nitrogen-oxygen double bond is opened, and the hydrogen-oxygen bond of the alcohol molecule is broken, and the nitric acid partially loses one molecule of water to form nitrogen. Oxygen double bond.

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This type of reaction is mainly used for the preparation of inorganic acid primary alcohol esters. The preparation of the inorganic acid tertiary alcohol ester is not suitable for this method because the tertiary alcohol is susceptible to elimination reaction when reacted with the inorganic acid. Reactivity order of alcohols

The reaction of an alcohol with an acid chloride and an acid anhydride of an oxy-inorganic acid also produces an inorganic acid ester.

Oxygenated inorganic acid esters have many uses. Ethylene glycol dinitrate and glycerol trinitrate (commonly known as nitroglycerin ) are strong explosives. Nitroglycerin can also be used for vasodilation, for the treatment of angina and biliary colic. Scientists have discovered that nitroglycerin can treat heart disease because it releases the messenger molecule “NO” and clarifies the mechanism of action of “NO” in life activities. To this end, they won the 1998 Nobel Prize in Physiology and Medicine.

Phosphate esters in the nucleotides of living organisms, such as the reaction of glycerophosphates with calcium ions, can be used to control the concentration of calcium ions in the body. If this reaction is dysregulated, it can cause rickets.

Alcohol hydroxyl substitution reaction

In Alcohol, the carbon-oxygen bond is a polar covalent bond. Since the electronegativity of oxygen is greater than that of carbon, the shared electron pair is biased toward oxygen. When the nucleophile attacks the positive carbon, the carbon-oxygen bond is split and the hydroxyl group is pro- Replace with nuclear reagents. One of the most important nucleophilic substitution reactions is the replacement of a hydroxyl group with a halogen atom. The commonly used methods are as follows:

  1. Reaction with hydrohalic acid

(1) General situation

The hydrohalic acid reacts with the alcohol to form an alkyl halide, in which the alcoholic hydroxyl group is replaced by a halogen atom. Reactivity order of alcohols

ROH+HX——>RX+H2O

The alcoholic hydroxyl group is not a good leaving group and requires the help of acid to protonate the hydroxyl group and leave it in the form of water. The reactivity of various alcohols is 3°>2°>1°, and the tertiary alcohol is easy to react. It can be reached only by shaking concentrated hydrochloric acid at room temperature. Hydrobromic acid can also react with tertiary alcohol at low temperature. As with hydrogen chloride, hydrogen bromide gas at 0 ℃ by three alcohol, the reaction can be completed within a few minutes, which is three common methods of alkyl halides.

  1. Reaction with phosphorus halide

The alcohol reacts with the phosphorus halide to form a halogenated alkane.

The alcoholic hydroxyl group is a poor leaving group and forms a reaction with phosphorus tribromide.

Br attacks the carbon atom of the alkyl group, and -OPBr2 leaves as a leaving group. – There are also two bromine atoms in OPBr2 that continue to react with the alcohol.

The iodide can be prepared from phosphorus triiodide and alcohol, but usually, the phosphorus triiodide is replaced by red phosphorus and iodine, and the alcohol, red phosphorus and iodine are heated together to form a phosphorus triiodide, and then reacted with the alcohol.

The chlorinated alkane is usually prepared by reacting phosphorus pentachloride with alcohol.

Among the above methods, the most commonly used ones are phosphorus tribromide and primary alcohol, β-position branched primary alcohol, secondary alcohol to form corresponding brominated alkane, secondary alcohol, and some reversible reactions. The temperature of the alcohol must be below 0 ° C to avoid rearrangement. Red phosphorus and iodine are often used in the first alcohol to make the corresponding iodide. [3]

  1. Reaction with thionyl chloride

If thionyl chloride is reacted with an alcohol, the chloroalkane can be directly obtained, and both sulfur dioxide and hydrogen chloride gas are generated, and these gases leave the reaction system during the reaction, which facilitates the reaction in the direction of product formation. Not only is the rate fast, but the reaction conditions are also mild, the yield is high, and no other by-products are formed. It is generally a good method for producing oxyalkylenes by using an excess of thionyl chloride and maintaining a slight boiling.

Preparation of halogenated hydrocarbons by the reaction of an alcohol with sulfonyl chloride in an intermediate stage

The alcoholic hydroxyl group must be subjected to a substitution reaction under the catalysis of a protic acid or a Lewis acid, and the acid moiety of the besylate is a good leaving group, and thus such an ester is more susceptible to a nucleophilic substitution reaction than Alcohol. Reactivity order of alcohols

This allows the primary or secondary alcohol to react with benzene sulfonyl chloride to form a sulfonate which is then converted to an alkyl halide with good purity. Sulfonyl chloride can be prepared by reacting the corresponding sulfonic acid with phosphorus pentachloride.

Oxidation of alcohol

The primary alcohol and the secondary alcohol have hydrogen on the carbon atom connected to the hydroxyl group of the alcohol, and can be oxidized to an aldehyde, a ketone or an acid; the carbon atom attached to the hydroxyl group of the tertiary alcohol has no hydrogen and is not easily oxidized, such as in an acidic condition. Underneath, it is easily dehydrated into an alkene, and then the carbon-carbon bond is oxidatively cleaved to form a small molecule compound.

Alcohol Properties:-

1. Alcohol का Boiling Point

2. Water Solubility

Alcohol में अगर H – Bonding बढ़ेगी तो Boiling point और Solubility (H 2 O ) भी बढ़ेगा

Reactivity order of alcohols

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