Carboxylic acid: physical properties.

Almost all homes have vinegar.And most people know that it is the basis of acetic acid.But it is from the chemical point of view?What other organic compounds of this series exist and what are their characteristics?Let's try to sort out this issue and explore the limits monobasic carboxylic acids.Especially in the home it is used not only acetic, but also some other, and only derivatives of these acids in general are frequent guests in every home.

class of carboxylic acids: general characteristics

From the point of view of science of chemistry, this class of compounds include oxygen-containing molecules that have a special group of atoms - a carboxyl functional group.It has the form -COOH.Thus, the general formula which have all limit monocarboxylic acid is as follows: R-COOH, wherein R - is a particle radical, which may include any number of carbon atoms.

According to this, the definition of this class of compounds can be given that.Carboxylic acid - is oxygenated organic molecules, which include one or more functional groups -COOH - carboxyl groups.

fact that these substances are specifically to acids, explains the mobility of the hydrogen atom in the carboxyl.The electron density is unevenly distributed, since oxygen - the most electronegative group.From this connection O-H highly polarized and hydrogen becomes extremely vulnerable.It is easily cleaved by entering into chemical reactions.Therefore acid corresponding indicator gives a similar reaction:

  • phenolphthalein - colorless;
  • litmus - red;
  • universal - red;
  • methyl orange - red and others.

Due to the hydrogen atom, carboxylic acids exhibit oxidizing properties.However, the presence of other atoms, allowing them to recover and participate in many interactions.


There are several key features, which are divided into carboxylic acid groups.The first of them - it is the nature of the radical.In this isolated factor:

  • Alicyclic acid. Example: quinine.
  • Aromatic. Example: benzoic.
  • aliphatic.EXAMPLE acetic, acrylic acid, oxalic acid and others.
  • Heterocyclic. Example: nicotine.

Speaking of bonds in the molecule, it is also possible to distinguish two groups of acids:

  • limits - all single bonds only;
  • unsaturated - Available double, one or more.

also feature classification can serve as functional groups.So, there are the following categories.

  1. monobasic - only one -COOH group.Example: formic, stearic, butyric, valeric and others.
  2. Dibasic - respectively, the two groups COOH.Example: oxalic, malonic, and others.
  3. Multibasic - citric, lactic, and others.

Later in this article we will only limit monobasic aliphatic carboxylic acids.

History of discovery

Winery thrived with the most ancient times.As is known, one of its products - acetic acid.Therefore the history of fame of this class of compounds has its roots from the time of Robert Boyle and Johann Glauber.However, the chemical nature of these molecules to find out for a long time without success.

For a long time dominated by the views of vitalists who denied the possibility of the formation of organic without living beings.But in 1670 AD Ray managed to get the very first representative - methane or formic acid.He did it by heating in a flask of live ants.

Later, the work of scientists Berzelius and Kolbe showed the possibility of synthesis of these compounds from inorganic substances (distillation, charcoal).The result was the acetic.Thus carboxylic acids were examined (physical properties, structure) and the beginning for the opening of all the other representatives of a number of aliphatic compounds.

physical properties

today studied in detail all their representatives.For each of these characteristics can be found in all parameters, including the use in industry and being in nature.We will examine what constitutes carboxylic acids, their physical properties, and other parameters.

So, there are several key characteristic parameters.

  1. If the number of carbon atoms does not exceed five, then this strongly smelling and volatile liquids movable.Above five - heavy oily substances, more - hard, parafinoobraznye.
  2. density of the first two representatives of more than one.All other lighter than water.
  3. Boiling point: the more the chain, the higher the score.The more branched structure, the lower.
  4. Melting point depends on the parity number of carbon atoms in the chain.At even higher than it, the odd below.
  5. dissolve in water very well.
  6. ability to form strong hydrogen bonds.

These features are explained by the symmetry of the structure, and hence the structure of the crystal lattice, its durability.The more simple and structured molecule, the above figures, which give the carboxylic acid.Physical properties of these compounds to identify areas and methods for use in industry.

chemical properties

As we have designated above, the acid can exhibit different properties.Their reactions are important for the industrial synthesis of many compounds.Let the most important chemical properties which may be monocarboxylic acids.

  1. Dissociation: R-COOH = RCOO- + H +.
  2. present an acid behavior, i.e. it interacts with the basic oxides and their hydroxides.With simple metals reacted by the standard procedure (i.e., only those that are to hydrogen in the electrochemical series).
  3. with stronger acids (inorganic) behaves as a base.
  4. ability to restore to the primary alcohol.
  5. special reaction - esterification.This is reacted with an alcohol to form a complex of the product - ester.
  6. decarboxylation reaction, ie the elimination of the compound molecule of carbon dioxide.
  7. capable of reacting with halides of elements such as phosphorus and sulfur.

obvious how multifaceted carboxylic acids.Physical properties, as well as chemical, are quite diverse.In addition, it should be said that in general, as the acid strength of all organic molecules are weak compared to their inorganic counterparts.Their dissociation constants do not exceed the figure 4.8.

Methods for producing

There are several ways that you can get the marginal carboxylic acids.

1. In the lab do oxidation:

  • alcohols;
  • aldehydes;
  • alkyne;
  • alkylbenzenes;
  • destruction of alkenes.

2. Hydrolysis:

  • esters;
  • nitrites;
  • amides;
  • trigalogenalkanov.

3. decarboxylation - elimination of CO2 molecules.

4. In industrial synthesis is carried out by oxidation of hydrocarbons with more carbon atoms in the chain.The process is carried out in several stages to yield a plurality of byproducts.

5. Some individual acids (formic, acetic, butyric, valeric, etc) receive specific way using natural ingredients.

basic compound limit carboxylic acid salt

salts of carboxylic acids - important compounds used in industry.They are prepared by reacting the latter with:

  • metals;
  • basic oxides;
  • amphoteric oxides;
  • alkalis;
  • amphoteric hydroxides.

Particularly important among them are those that are formed between the alkali metals sodium and potassium and the higher marginal acids - palmitic, stearic.For products such interaction - soap, liquid and solid.


So if we are talking about such a reaction: 2C17H35-COOH + 2Na = 2C17H35COONa + H2,

the resulting product - sodium stearate - it is by nature a normal soap used for washing clothes.

If you replace the palmitic acid to, and potassium metal on, you get potassium palmitate - liquid soap for washing hands.Therefore, we can confidently state that the salts of carboxylic acids - this is actually important compounds of organic nature.Their manufacturing and use of a colossal in scope.If you imagine how much soap to spend every person on Earth, it is easy to imagine, and these scales.

carboxylic acid ester

special group of compounds, which has its place in the classification of organic substances.This class of esters.They are formed by the reaction of carboxylic acids with alcohols.The name of such interactions - esterification.General view can be represented by the equation:

R, -COOH + R "-OH = R, -COOR" + H2O.

product with two radicals is an ester.Obviously, in the reaction the carboxylic acid, alcohol, ester and water have undergone significant changes.Thus, hydrogen leaves from the acid molecules in the form of a cation and meets with a hydroxy group from an alcohol being split off.This results in a molecule of water.Grouping, the rest of the acid attaches itself to a radical of the alcohol to form an ester molecule.

What is so important these reactions and what the commercial value of their products?The fact is that esters are used as:

  • nutritional supplements;
  • flavors;
  • integral component of perfume;
  • solvents;
  • components of varnishes, paints, plastics;
  • medicines and so on.

It is clear that the field of use are wide enough to justify production volumes in the industry.

ethanoic acid (vinegar)

This limit monobasic aliphatic carboxylic acid, which is one of the most popular in terms of production worldwide.Its formula - CH3COOH.Such prevalence it owes its properties.After all, the field of use is very wide.

  1. It is a food additive under code E-260.
  2. used in the food industry for preservation.
  3. is used in medicine for the synthesis of pharmaceuticals.
  4. component in the preparation of aromatic compounds.
  5. solvent.
  6. participants in the process of printing, dyeing fabrics.
  7. necessary components in the plurality of chemical synthesis substances.

In a life of its 80-percent solution called acetic essence, as if to dilute it to 15%, it will turn out just vinegar.Pure 100% acetic acid is called the ice.

Formic acid

The first and simplest representative of this class.Formula - HCOOH.It is also a food additive under code E-236.Her natural sources:

  • ants and bees;
  • nettle;
  • needles;
  • fruit.

Main field of use:

  • for preservation and preparation of animal feed;
  • used for pest control;
  • for dyeing fabrics, etch parts;
  • as a solvent;
  • bleach;
  • in medicine - for disinfection of instruments and equipment;
  • to produce carbon monoxide in the laboratory.

also in surgery of the acid solutions used as antiseptics.