Please ask the master of organic chemistry from the university to answer an inductive question.

1._ master the structure of carboxyl and the chemical properties of carboxylic acid.

2._ Master the influence of induction effect and * * * yoke effect on the acidity of carboxylic acid.

3._ Master the preparation method of carboxylic acid.

4. Understand the main uses of important carboxylic acids.

5._ Understand the characteristic reaction of dicarboxylic acid substituted carboxylic acid.

Learning requirements

Learning content

Brief introduction of carboxylic acid compounds

Classification, Naming and Structure of Carboxylic Acid

Physical and spectral properties of carboxylic acids

Chemical properties of carboxylic acids

Sources and preparation of carboxylic acids

Important monocarboxylic acid

dicarboxylic acid

Substituted acid

acid base theory

List of chemical characteristics

Carboxylic acid can be regarded as a compound generated by the substitution of hydrogen atoms in hydrocarbon molecules by carboxyl groups (-COOH). Its general formula is RCOOH. The functional group of carboxylic acid is carboxyl.

Ibuprofen

Aspirin

Carboxylic acid is the final product of oxidation of many organic compounds, which is ubiquitous in nature (in the form of esters) and widely used in industry, agriculture, medicine and people's daily life.

Brief introduction of carboxylic acid compounds

Therefore, the structure of carboxyl group is a P-π * * yoke system.

Section 1 Classification, Naming and Structure of Carboxylic Acids

First, the structure.

When carboxyl groups are ionized into negative ions, oxygen atoms are negatively charged, which is more conducive to the yoke, so carboxylic acids are easily dissociated into negative ions.

Because the carboxyl group is not a simple addition of carbonyl group and hydroxyl group, there is neither a typical carbonyl group nor a typical hydroxyl group in the carboxyl group, but a unity of the two.

The properties of carboxylic acids can be predicted from the structure, and there are the following categories:

reduction reaction

Second, naming

1, common name

Tartaric maleic acid

Formic acid,

Formic acid benzoic acid oxalic acid succinic acid (succinic acid)

Citric acid (3- hydroxy -3- carboxyglutaric acid)

Cinnamic acid (3- phenylacrylic acid)

()

A takes the longest carbon chain containing carboxyl as the matrix and is named' A' acid according to the number of carbon atoms in the main chain.

B. number. Count from carboxyl carbon atoms. (Use Arabic numerals or Greek letters. )

C. If there are unsaturated bonds, indicate the grade of alkene (or alkyne) bonds, and the main chain includes double bonds and triple bonds. Write the rank, number and name of the substituent before the mother name, number and name in turn.

Alicyclic carboxylic acid. As long as the word carboxylic acid is added after alicyclic hydrocarbon, complex rings can be used as substituents.

E. aromatic acids can be called aryl substitutes of fatty acids.

F polycarboxylic acid: choose a carbon chain with two carboxyl groups as the main chain, and call it dibasic acid according to the number of C atoms.

2. Systematic nomenclature

-ethoxyacetic acid

4- methyl -4- phenyl -2- pentenoic acid

propanoic acid

(3- oxopropionic acid or 3- carbonyl propionic acid)

3- butyric acid

(3- oxobutyric acid or acetoacetic acid)

(1R, 3R)- 1, 3- cyclohexanedicarboxylic acid

Third, classification

1. According to the type of hydrocarbon family, it can be divided into:

A. aliphatic carboxylic acids: saturated carboxylic acids, unsaturated carboxylic acids

B, alicyclic carboxylic acid

aromatic acids

2. According to the number of carboxyl groups, it can be divided into monocarboxylic acids, dicarboxylic acids and polycarboxylic acids.

Saturated acid

Unsaturated acid

aromatic acids

Monobasic acid

acetic acid

acrylic acid

benzoic acid

binary acid

oxalic acid

Maleic acid salt

O-dibenzoic acid

solubility

Physical properties of carboxylic acids

Status: C 1~C3 pungent sour liquid, soluble in water.

C4~C9 are oily liquids with sour taste, which are insoluble in water.

& gtC9 waxy solid, odorless.

Dicarboxylic acids and aromatic acids are crystals.

Carboxylic acid is a polar molecule, which can form hydrogen bonds with water, so the lower monobasic acid (C 1 ~ C4) is miscible with water. However, the solubility of n-valeric acid with molecular weight ↑ in water is only 3.7%. C 10 carboxylic acid is insoluble in water, binary acid is soluble in water, and the solubility of aromatic acid is very small. The solubility of benzoic acid is 0.34g/ 100gH2O.

melting point

(1) melting point: monocarboxylic acid starts from C6 and increases zigzag with molecular weight ↑. Melting point of carboxylic acid with even carbon atoms; The melting point of two adjacent homologues is a hyperbola of melting point, which is mainly due to the high symmetry of even carbon, orderly molecular arrangement in the crystal, large lattice energy and high melting point.

② boiling point

The boiling point of linear saturated monocarboxylic acid is higher than that of alcohols with similar molecular weight, such as formic acid and ethanol, with molecular weight of 46 and boiling points of 100.5℃ and 78.3℃ respectively. The molecular weight of acetic acid and propanol is 60, and their boiling points are 1 17.9℃ and 97.2℃ respectively.

The main reasons are as follows: carboxylic acids are associated with each other through hydrogen bonds, and a) the bond energy is greater than that between alcohols. (The bond energy of hydrogen bond in acid is 30kJ/mol, and that in alcohol is 25kJ/mol. B) Lower acids also exist in the form of dimer in steam, so the boiling point is high.

IR: two functional groups reflecting -C=O and -OH.

RCH2COOH R2CHCOOH

1HNMR:RCOOH

Spectral properties of carboxylic acids

Chemical properties of carboxylic acids

The properties of carboxylic acids can be predicted from the structure, and there are the following categories:

First of all, acidity

Secondly, the substitution reaction of hydroxyl group (OH) to carboxyl group.

Third, decarboxylation reaction.

Halogenation of Tetra, α-H

Verb (abbreviation of verb) reduction of carboxylic acid

Carboxylic acid is more acidic than water, alcohol and even carbonic acid.

The RCOO- negative ion generated by the dissociation of carboxylic acid is stable and easy to generate due to the existence of the * * * yoke effect, and the negative charge on the oxygen atom is evenly dispersed on the two atoms.

First of all, acidity

The acidity of carboxylic acid is as follows:

Carboxylic acid can react with alkali to form salt and decompose carbonate.

This characteristic can be used for the identification and separation of alcohols, phenols and acids. Water-insoluble carboxylic acids are soluble in NaOH and NaHCO3, while water-insoluble phenols are soluble in NaOH and NaHCO3, and water-insoluble alcohols are soluble in NaOH and NaHCO3. Organic compounds containing carboxyl groups can increase their water solubility in alkali. For example, penicillin G is an organic substance containing carboxyl groups, which is insoluble in water. Generally, it is made into potassium sodium salt to increase its water solubility and easy absorption.

Factors affecting the strength of carboxylic acid

1, the influence of electronic effect on acidity

2. Effect of substituent position on acidity of benzoic acid

3, the influence of field effect

1, the influence of electronic effect on acidity

The induced effect of 1 electron absorption enhanced the acidity.

FCH2COOH & gtClCH2COOH & gtBrCH2COOH & gtICH2COOH & gtCH3COOH

The PKa value is 2.66 2.86 2.89 3. 16 4.76.

The induction of electron donor weakened the acidity.

CH3COOH & gtCH3CH2COOH & gt(CH3)3c ooh

PKa value 4.76 4.87 5.05

3 the electron-withdrawing group increases and the acidity increases.

ClCH2COOH & gtCl2CHCOOH & gtCl3CCOOH

The PKa value is 2.86 1.29 0.65.

1) induced effect

2) *** Yoke Effect When carboxyl groups can be conjugated with other groups, the acidity is enhanced.

The farther the electron-withdrawing group is from the carboxyl group, the less acidic it is.

ethyl acetate

④(OH)-I rch 2 OH & gt； R2CHOH & gtR3COH

Hcooh > when alcohol is the same; CH3COOH & gtRCH2COOH & gtR2CHCOOH & gtR3CCOOH

(3) Esterification mode

In the process of esterification, there are two different dehydration modes between carboxylic acid and alcohol:

Which method of dehydration depends on the structure and reaction conditions of carboxylic acid and alcohol. Isotopic labeling of alcohol confirms this:

Esterification of carboxylic acids with primary and secondary alcohols is based on the cleavage of acyl oxygen bonds.

Esterification of tertiary alcohols with carboxylic acids is based on the cleavage of alkoxy bonds.

There is no O 18 in H2O, which indicates that the reaction is acyl oxygen cracking.

(4) esterification reaction process

1 2 alcohol is an acyl oxygen cleavage process,

Alcohol (tertiary alcohol) is the process of alkoxy cracking.

CH3COOH + SOCl2 CH3COCl + SO2 + HCl

Phosphorous acid is not volatile, so this method is suitable for preparing low boiling point acyl chloride.

The boiling point of phosphoryl chloride is low (105.3℃), which is suitable for preparing high-boiling acyl chloride.

The by-products of this method are all gases, which is beneficial to separation and has high yield.

2. Formation of acid halide

Carboxylic acid reacts with PX3, PX5 and SOCL 2 to form acid halide.

Acetic anhydride is often used as dehydrating agent to prepare anhydride because it can react with water quickly and is cheap, and the generated acetic acid is easy to remove.

The binary acids 1, 4 and 1, 5 can be heated to generate cyclic (five-or six-membered) anhydrides without any dehydrating agent.

3. Generation of acid anhydride

Carboxylic acid is heated and dehydrated under the action of dehydrating agent to generate anhydride.

Asymmetric anhydride is prepared by the reaction of carboxylate and acyl chloride.

For example:

When the diammonium salt of dibasic acid is heated, intramolecular dehydration and deamination occur, resulting in five-membered or six-membered cyclic imide.

4. Generation of amide

Ammonium carboxylate can be obtained by introducing ammonia gas into carboxylic acid or adding RNH and r2nh, and ammonium carboxylate can be hydrolyzed to generate amide.

Third, decarboxylation reaction.

When heated under certain conditions, carboxylic acid will undergo decarboxylation reaction.

Saturated monocarboxylic acids are difficult to decarboxylate when heated, but metal salts of lower carboxylic acids can decarboxylate when heated in the presence of alkali.

Hen-Sdic reaction: The reaction of decarboxylation of silver carboxylate in the presence of bromine or chlorine to form alkyl halide.

This reaction can be used to synthesize halogenated hydrocarbons with one carbon less than carboxylic acid.

Carboxylic acid can also react with HgO+Br2 to obtain halogenated hydrocarbons, which is called Crystal reaction.

The reaction between carboxylic acid and (ch3coo) 4ppbLiCl to form chlorinated hydrocarbons is called Koch reaction.

The alpha carbon atom of monocarboxylic acid is connected with -NO2 and -C≡N,

Decarboxylation is easy to occur when strong electron-withdrawing groups such as -co- and -cl.

Some aromatic carboxylic acids can not only decarboxylate, but also be easier than saturated monobasic acids.

At present, ketones can be directly prepared by gas-phase catalytic decarboxylation of carboxylic acids.

Electrolytic carboxylate solution can produce alkyl coupling at anode to generate hydrocarbons.

This reaction is called kolbe reaction.

Colbert reaction is also used to electrolyze dibasic acid monoesters to produce long-chain dibasic acid esters.

Is one of the successful examples.

The α -hydrogen atom of aliphatic carboxylic acid can also be replaced by halogen atom, but its reaction activity is much lower than that of aldehyde and ketone, and it can usually be carried out in the presence of a small amount of red phosphorus, sulfur and other catalysts.

By controlling the conditions, the reaction can stay in the substitution stage.

Halogenation of Tetra, α-H

α -halogenated acids are very active and can undergo nucleophilic substitution and elimination reactions, such as:

Carboxylic acid is not easy to be reduced, but under the action of strong reducing agent LiAlH4, carboxyl group can be reduced to hydroxyl group, resulting in the corresponding 1 Roh.

This method not only has high yield, but also does not affect the existence of C=C and C ≡ C, and can be used for the reduction of unsaturated acids.

Verb (abbreviation of verb) reduction of carboxylic acid

Diborane can also reduce carboxyl groups to primary alcohols.

Sources and preparation of carboxylic acids

Source: Carboxylic acids are widely found in nature, and almost all common carboxylic acids have a common name. Most carboxylic acids in nature exist in the form of esters in oils, fats, (higher fatty acid glycerides) and waxes (higher fatty acid monoesters). After oil, fat and wax are hydrolyzed, a mixture of various carboxylic acids can be obtained.

Method:

First, oxidation method

Second, carboxylation method

Thirdly, hydrolysis method.

(a) Oxidation of hydrocarbons-Only α-H aromatic hydrocarbons can be oxidized to benzoic acid.

(2) Oxidation of primary alcohols or aldehydes-preparation of carboxylic acids with the same carbon number.

I. Oxidation method

Preparation of carboxylic acid by oxidation-reduction of a carbon atom with methyl ketone

(d) Oxidation of olefins and alkynes-Applicable to symmetric olefins, alkynes and terminal olefins and alkynes.

(5) Aldehydes without α-H can be heated in concentrated alkali to obtain acids and alcohols.

Cyclic ketones can be oxidized to lactones and then to diacids.

(3) Oxidation of ketones

Second, carboxylation method

(1) Grignard reagent reacts with CO2 to prepare carboxylic acid with one additional carbon atom.

(2) Carbonylation of olefins-adding a carbon atom to prepare carboxylic acid.

Olefin absorbs CO and H2O in the presence of Ni(CO)4 catalyst to produce carboxylic acid.

1, 2, 3 Rx can be used, but vinyl halogenated hydrocarbons are difficult to react.

Thirdly, hydrolysis method.

This method is only applicable to1rx (2,3 rx is easy to react with NaCN).

1._

(2) Hydrolysis of carboxylic acid derivatives

Oil and carboxylic acid derivatives get carboxylic acid, by-products glycerol and alcohol.

(3) Synthesis of various carboxylic acids by ethyl acetoacetate and diethyl malonate.

(4) Kolbe-Schmidt reaction-adding a carbon atom to prepare phenolic acid.

Hydrolysis of (1) nitrile-preparation of carboxylic acid by adding a carbon atom.

Important monocarboxylic acid

formic acid

1. structure

2. Features

① The acidity of formic acid is obviously higher than that of other saturated monobasic acids.

Formic acid can be reduced and can produce silver mirror reaction.

Formic acid can also change the color of potassium permanganate solution.

Formic acid has bactericidal power and can be used as disinfectant or preservative.

⑤ Formic acid is decomposed into carbon monoxide and water when heated with concentrated sulfuric acid.

Acetic acid and benzoic acid

Enact laws

The formic acid aqueous solution cannot be distilled to obtain pure formic acid, but it should be used.

Anhydrous sodium formate is distilled in formic acid containing sulfuric acid. or

First, physical properties

1. Dicarboxylic acids are solid crystals, and their melting points are much higher than those of monocarboxylic acids with similar molecular weight. With the increase of the number of carbon atoms, the melting point tends to decrease, and even carbon atoms are higher than odd carbon atoms.

2. The solubility is greater than that of the corresponding monobasic acid, and it is soluble in ethanol and insoluble in other organic solvents.

Second, the chemical properties of dicarboxylic acids

Third, important dicarboxylic acids.

Oxalic acid (oxalic acid) is reducible and easily oxidized into carbon dioxide and water.

adipic acid

butene diacid

phthalic acid

dicarboxylic acid

Second, the chemical properties of dicarboxylic acids

1. has the generality of carboxylic acid.

For acidity, ka 1 >: Ka2 or PKA1< pka2.

For cis-and trans-butenedioic acids

For acidity: Ka 1 (cis) > ka 1 (anti); Ka2 (anti) > ka2 (cis)

Cis-trans structures are also different in other physical properties, such as: the water solubility of cis is greater than that of trans (cis has a large dipole moment), and the melting point of trans is higher than that of cis (trans has a high symmetry and a large lattice energy).

2. The heating reaction law of dicarboxylic acid.

Blank's Law: Under the condition that cyclic compounds can be formed, it is always easier to form five-membered or six-membered cyclic compounds (that is, five-membered and six-membered rings are easy to form).

(1) Oxalic acid and malonic acid are decarboxylated by heating to form monoacid.

(2) succinic acid and glutaric acid are dehydrated (not decarboxylated) by heating to produce cyclic anhydride.

(3) When heated, adipic acid and pimelic acid are dehydrated and decarboxylated to form cyclic ketones.

3. Reaction with diol

Cyclic esters (but only five-membered rings or six-membered rings) can be generated by the reaction of dibasic acids with dibasic alcohols.

Polyester can also be produced.

(1) oxalic acid and malonic acid are decarboxylated by heating to generate monobasic acid,

(2) succinic acid and glutaric acid are dehydrated (not decarboxylated) by heating to generate cyclic anhydride,

(3) heating adipic acid and pimelic acid for dehydration and decarboxylation to form cyclic ketone,

Substituted carboxylic acid

Substituted acid is a compound formed after the hydrogen atom on the hydrocarbon group in carboxylic acid molecule is replaced by other atoms or subunits.

Substituted acids include halogenated acids, hydroxy acids, amino acids and carbonyl acids, among which halogenated acids and amino acids will be discussed in relevant chapters, and only hydroxy acids and carbonyl acids will be discussed here.

oxyacid

1. production method

2. Properties of hydroxy acids

3. Important hydroxy acids (self-study)

Second, carbonyl acid

Compounds containing carbonyl and carboxyl groups in the molecule are called carbonyl acids, such as pyruvate and 3- butyric acid.

1) Hydrolysis of Halogenated Acids When α, β, γ and other halogenated acids are treated with alkali or silver hydroxide, corresponding hydroxy acids can be generated.

Method for preparing beta-hydroxy acid by Reformatsky reaction.

2) hydrolyzing cyanohydrin to prepare alpha-hydroxy acid.

Preparation method of 1, hydroxy acid

It has the characteristics of alcohol and acid, and also has a characteristic reaction due to the mutual influence of the relative positions of hydroxyl and carboxyl, mainly in the law of heating reaction.

When β -hydroxy acid is heated, intramolecular dehydration occurs, and α -β is mainly generated.

Unsaturated carboxylic acid.

When α -hydroxy acid is heated, two molecules are esterified with each other to form esters.

2. Properties of hydroxy acids

γ-and δ-hydroxy acids are heated to form five-membered and six-membered cyclic lactones.

α-and β-hydroxy acids also have the property of decarboxylation after oxidation.

Degradation of α-and β-hydroxy acids;

This is a method for preparing higher aliphatic aldehydes and ketones.

_ _ _ _ _ hydroxy acids in nature

① Lactic acid:

Structure:

Existence: yogurt (racemic), sucrose fermentation (left-handed), muscle (right-handed).

Uses: Strong hygroscopicity; Used as calcium remover in industry (calcium salt is insoluble in water); Used as acid enhancer in food industry; Calcium salt can supplement calcium.

② Malic acid (α-hydroxy acid)

Structure: _

Existence: in immature fruit; In the leaves of plants; What exists in nature is left-handed

Uses: Pharmaceutical and food industries.

(3) stone acid.

structure

Existence: in all kinds of fruits; Or the salt in the fruit.

Uses: It can be used as sour agent, and its antimony potassium salt has anti-schistosomiasis effect.

④ Citric acid

Structure:

Existence: in the fruits of many plants; Colorless crystals exist in animal tissues and body fluids.

Uses: Condiment (acid) in food industry, also used in pharmaceutical industry.