Andehit là gì? Đặc điểm cấu tạo, tính chất, cách điều chế và ứng dụng

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Andehit is a compound that plays an important role in life and is a raw material for a number of industries. So what is aldehyde? In this article, Monkey will help you synthesize the most complete and detailed knowledge about aldehydes through the structure, properties, preparation and application of this compound.

What is the definition of Andehit? Characterization of aldehyde structure

An aldehyde is an organic compound in which the –CH=O group is bonded to a carbon atom or a hydrogen atom. In other words, aldehyde is the product obtained after the H atom in the hydrocarbon is replaced by the –CHO group. In this case, the –CH=O group is called the Andehit functional group.

Some examples of Andehit:

  • HCH=O: Formic aldehyde or Metanal.
  • CH3CH=O: Acetic aldehyde or Ethanal.
  • C6H5CH=O: Benzoic aldehyde or Benzaldehyde.
  • O=CH-CH=O: Oxalic aldehyde

Andehit’s structural formula:

In the -CHO group, the C=O double bond consists of a strong σ bond and a less stable π bond, similar to the C=C bond in an alkene molecule, so that the aldehyde has some properties in common with the alkene.

General aldehyde formula:

  • CxHyOz: In which, x, y, z are positive integers; y is an even number satisfying the condition 2 ≤ y ≤ 2x + 2 – 2z and z ≤ x. This is the formula commonly used to write the combustion reaction.

  • CxHy(CHO)z or R(CHO)z: This formula is often used to write reactions that occur in the CHO group.

  • CnH2n+2-2k-z(CHO)z (where k = number of p bonds + number of rings): This formula is often used when writing addition reactions of H2 or addition of Br2.

Classification of aldehydes

Based on the structural characteristics of the hydrocarbon radical and the number of –CHO groups in the molecule, aldehydes are divided into 5 different types:

For example:

Saturated, open-chain, monofunctional aldehyde is a compound in a molecule that has a -CHO group attached to an alkyl radical or a hydrogen atom. Substances H-CH=O, CH3-CH=O, CH3-CH2-CH=O… form a homologous series of aldehydes, open-chain, monofunctional with:

The formula of aldehydes according to each of the above classifications:

  • Andehit, monofunctional, open circuit: CnH2n+1CHO (n≥0) or CmH2mO (m≥1)

  • Andehit saturated, polyfunctional, open circuit: CnH2n(CHO)2 (n≥0) or CmH2m-2O2 (m≥2)

  • Unsaturated aldehyde, containing C=C double bond, open-chain monofunctional: CmH2m-2O (m≥3)

How to name aldehydes

Names of some common aldehydes = Andehit + corresponding acid name.

Alternative names for saturated, monofunctional, open-chain aldehydes = Name of saturated hydrocarbon corresponding to main chain + al. In which, the main chain of the aldehyde molecule is the longest carbon chain starting from the -CHO group.

Examples of naming aldehydes.  (Photo: Internet Collection)

Let’s find out the nomenclature of some common Andehit no, monofunctional, open circuit in the following table:

Nomenclature of some common, monofunctional, open-circuit aldehydes.  (Photo: Internet Collection)

In addition, we also need to note a special case in naming: HCHO solution 37% – 40% is called formalin or formon.

Physical properties of aldehydes

What are the properties of aldehydes? Then here are some typical physical properties of aldehydes that you need to remember:

Learn the properties of aldehydes.  (Image:

  • Existence state: Under normal conditions, homologous series aldehydes exist as gases (HCHO boils at -19 degrees Celsius and CH3CHO boils at 21 degrees Celsius), very soluble in water. The next aldehydes are liquid or solid, the solubility in water decreases with increasing molecular mass.

  • Boiling point: The boiling point of aldehydes is lower than that of alcohols of the same mass due to the absence of hydrogen bonds in the molecule and higher than that of hydrocarbons with the same number of C atoms.

  • The aqueous solution of formic aldehyde is formon.

  • Saturated solution of formic aldehyde concentration 37 – 40% is formaline.


Chemical properties of aldehyde

The characteristic chemistry of iron aldehydes is evident in the hydrogen addition and incomplete oxidation reactions.

Hydrogen addition reaction

Adding hydrogen to a C=O double bond is the same as adding a C=C double bond:

CH3-CH=O (acetic aldehyde) + H2 → CH3-CH2-OH (ethyl alcohol) (Condition: Temperature, Ni catalyst)

The general reaction is as follows:

RCHO + H2 → RCH2OH (temperature, Ni catalyst)

Thus, when reacting with H2, the aldehyde acts as an oxidizing agent. If the origin R has π bonds, then H2 will add to those π bonds.

Incomplete oxidation reaction

Experiment: Put 1ml of AgNO3 1% into a test tube, add NH3 solution drop by drop, shake well until the solution is clear. Continue to add a few drops of aldehyde and gently boil for a few minutes at 60-70 degrees C. We observe that the wall of the test tube has a layer of bright metallic silver.

The reaction is as follows:

HCHO + 2AgNO3 + 3NH3 + H2O → H-COONH4 + 2Ag + 2NH4NO3 (temperature)

General equation: R-CH=O + 2AgNO3 + 3NH3 + H2O → R-COONH4 + 2Ag + 2NH4NO3 (temperature)

In this reaction, the Ag+ ion is reduced to an Ag atom with formic aldehyde as the reducing agent. This is also known as the silver coating reaction.

Thus, aldehydes both exhibit oxidizing properties (the aldehydes convert to the corresponding carboxylic acids) and the reducing properties (the aldehydes convert to the corresponding primary alcohols).

See more:

How to recognize aldehydes

We can recognize aldehydes through:

  • The ability of aldehydes to form shiny precipitates with AgNO3/NH3.

  • Ability to form brick red precipitate with Cu(OH)2 at high temperature

  • Discoloration of aqueous bromine solution. In the case of HCHO, reacting with the bromine solution produces CO2 gas.

2 ways to prepare aldehyde

How is aldehyde prepared? Join Monkey to learn 2 popular ways to prepare aldehydes:

How is aldehyde prepared?  (Photo: Internet Collection)

Preparation of aldehydes from alcohols

Oxidation of primary alcohol gives the corresponding aldehyde:

R-CH2OH + CuO → R-CHO + H2O + Cu

Example: CH3-CH2OH + CuO → CH3-CHO + H2O + Cu (temperature)

Preparation of aldehydes from hydrocarbons

In industry, aldehydes are prepared by three main methods:

CH4 + O2 → HCHO + H2O (temperature)

2CH2=CH2 + O2 → 2CH3-CHO (temperature, catalyst)


4 popular applications of aldehyde

Andehit has many applications in life, especially in the manufacturing industry. Some outstanding applications of aldehydes can be mentioned as:

Formaldehyde has important applications in the production of poly or urea-formaldehyde resins.  (Photo: Internet Collection)

  • Formaldehyde: Mainly used in the production of poly resin (phenol formaldehyde) or urea-formaldehyde, as a plasticizer and used for the synthesis of dyes and pharmaceuticals.

  • Formalin: A solution of 37 -40% formaldehyde in water is called formaline. It is mainly used for soaking animal carcasses, tanning or disinfecting, disinfecting, etc. Aqueous solution of formaldehyde is also used as a disinfectant. , soak animal samples as templates. They have antiseptic properties, so they are also used in the footwear industry.

  • Acetic aldehyde: Used to produce acetic acid – a raw material for many manufacturing industries.

  • Natural aldehydes: Used as flavorings in the food and cosmetic industries such as vanillin, piperonal, geranial (in rose essential oil), citrolenal (in eucalyptus essential oil).

Exercises on Andehit Acetic Textbook with detailed explanations

Some exercises on Andehit on pages 203, 204 of the 11th Chemistry Textbook below will help readers review the above knowledge in-depth through good and concise solutions.

Exercises on Andehit acetic textbook with detailed explanations.  (Photo: Internet Collection)

Solve lesson 2 of Chemistry textbook 11 pages 203

Write chemical equations to show that aldehydes are both oxidizing and reducing agents.

Suggested answer:

RCHO + H2 → RCH2OH (1) (temperature, catalyst)

2RCHO + O2 → 2RCOOH (2) (temperature, catalyst)

In (1), the aldehyde acts as an oxidizing agent

In (2), the aldehyde acts as a reducing agent.

Solve lesson 3 of the textbook on page 203 Chemistry 11

Complete the following series of transformations with the chemical equations:

Methane → methyl chloride → methanol → methanol → formic acid

Suggested answer:

The chemical equation of the transformation series:

Solve lesson 3 of the textbook on page 203 of Chemistry 11. (Photo: Collecting Internet)

Solve problem 5 Chemistry 11 textbook page 203

For 50.0 grams of acetic aldehyde solution, react with AgNO3 solution in NH3 (enough) to obtain 21.6 grams of Ag precipitate. Calculate the % concentration of acetic aldehyde in the solution used.

Suggested answer:

CH3CHO + 2AgNO3 + 3NH3 + H2O → CH3COONH4 + 2Ag↓ + 2NH4NO3

From the equation we have:

Solve problem 5 Chemistry 11 Textbook page 203. (Photo: Collecting Internet)

Solve lesson 6 Chemistry grade 11 textbook page 203

Write T (true) or F (false) in the blank next to the following sentences:

a. An aldehyde is a reducing agent only.

b. The aldehyde adds hydrogen to form a primary alcohol.

c. The aldehyde reacts with a solution of silver nitrate in ammonia to produce metallic silver.

d. Saturated, monofunctional, open-chain aldehydes have the general molecular formula CnH2nO.

e. When reacting with hydrogen, ketones are reduced to secondary alcohols.

Suggested answer:

a. Wrong because aldehyde has both reducing and oxidizing properties

b. True because RCHO + H2 → RCH2OH

c. True because RCH=O + 2AgNO3 + H2O + 3NH3 → RCOONH4 + 2NH4NO3 + 2Ag

d. It is true because the structure of a monosaturated acid contains an open circuit: CnH2nO

e. True because R1-CO-R2 + H2 → R1-CH(OH)-R2

Solution 7 Chemistry grade 11 textbook page 203

A mixture of 8.0 grams of a mixture of two consecutive aldehydes in the homologous series of saturated, monofunctional, open-chain aldehydes reacts with silver nitrate in ammonia solution (with excess) to obtain a precipitate of 32.4 grams of silver. Determine the molecular formula, write the structural formula and name the aldehydes.

Suggested answer:

Case 1: Two aldehydes are HCHO and CH3CHO

We have:

Solve lesson 7 Chemistry grade 11 textbook page 203. (Photo: Internet Collection)

Case 2: Mixture of two aldehydes without HCHO.

Solve lesson 7 Chemistry grade 11 textbook page 203. (Photo: Internet Collection)⇒ The two aldehydes are: CH3CHO (etanal) and C2H5CHO (etanal)

aldehyde exercises for students to practice on their own

Lesson 1: Completely burn 10.8 grams of a saturated aldehyde, an open circuit requires 10.08 liters of O2 gas (equipment). The product of combustion is passed through an aqueous solution of lime in excess of 45 grams of precipitate formed. What is the molecular formula of aldehydes?

Exercise 2: Complete combustion of 1 mole of organic compound X, yielding 4 moles of CO2. Substance X reacts with Na, participates in silver coating reaction and Br2 addition reaction in a mole ratio of 1: 1. Find the structural formula of X.

Lesson 3: What is the volume of H2 (0∘C and 2 atm) just enough to react with 11.2 grams of acrylic aldehyde?

Exercise 4: Complete hydrogenation of a mixture M consisting of two aldehydes X and Y no, monofunctional, open-chain, successive in a homologous series (MX

Exercise 5: For 7 grams of substance A with CTPT C4H6O react with excess H2 catalyzed to form 5.92 grams of isobutylic alcohol. What is A’s name? What is the yield of the reaction?

Lesson 6: Mixture A consists of acrylic aldehyde and a monofunctional aldehyde. Put all the burned products completely absorbed into the excess Ca(OH)_2Ca(OH)2 solution, obtaining 104 grams of precipitate. What is the reduced structural formula of X?

Lesson 7: Incomplete oxidation of 4.6 grams of a saturated alcohol, with CuOCuO, is heated to obtain 6.2 grams of mixture X consisting of aldehydes, water and residual alcohol. Let the entire mixture X react completely with the excess of AgNO_3AgNO3 solution in heated NH_3NH3 to obtain mg AgAg. What is the value of m?

Exercise 8: A mixture X includes acetylene, formic aldehyde, formic acid and H_2H2. Take z mol of mixture X through NiNi, heat it to obtain a mixture of Y consisting of organic substances and H_2H2. Complete combustion of mixture Y and then absorb all combustion products with lime water in the residue, after the reactions occur completely, 15 grams of precipitate are obtained and the volume of lime water solution is reduced by 3.9 grams. What is the value of z?

Lesson 9: Mixture X includes acetic aldehyde, butiric acid, ethylene glycol and acetic acid, in which acetic acid accounts for 27.13% by mass of the mixture. Burning 15.48 grams of mixture X obtained V liters of CO_2CO2​ (dktc) and 11.88 grams of H_2OH2​O. Absorb V liters of CO_2CO2 (dktc) into 400 ml dd of NaOHNaOH x mol/l to obtain solution Y containing 54.28 grams of solute. What is the value of x?

Lesson 10: Complete hydrogenation of a mixture M consisting of two aldehydes X and Y no, monofunctional, open-chain, consecutive in a homologous series (M_XMX < M_YMY), yielding a mixture of two alcohols with greater mass mass M is 1 gram. Complete combustion of M yields 30.8 grams of CO_2CO2. What is the formula and mass percent of X, respectively?

Hopefully the above article has provided readers with the most important basic knowledge about aldehydes. Monkey hopes that this information will help you better understand aldehydes and be able to apply this knowledge fluently in Chemistry exercises as well as in real life. CLICK “GET UPDATES” at the top of the page so you don’t miss out on other exciting Chemistry lessons!

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