Dicarboxylic acids are substances with two functional monovalent carboxyl groups - COOH, the function of which is to determine the basic properties of these substances.
Their general formula is HOOC-R-COOH. And here, by “R” is meant any organic 2-valent radical, which is atoms connected to the functional group of the molecule. However, this can be more detailed.
Physical properties
Dicarboxylic compounds are solids. The following physical properties can be distinguished:
- Excellent solubility in water. In this case, hydrogen intermolecular bonds are formed.
- The solubility limit in H 2 O is in the range of C 6 -C 7 . And this is understandable, because the content of the carboxyl polar group in the molecules is significant.
- They are poorly soluble in solvents of organic origin.
- They melt at much higher temperatures than alcohols and chlorides. This is due to the high strength of their hydrogen bonds.
- If the carboxyl compounds are heated, they will begin to decompose with the release of various substances.
Chemical properties
They are exactly the same for carboxylic acids as for monocarboxylic acids. Why? Because they also have a carboxyl group. It, in turn, consists of two elements:
- Carbonyl . > C = O. Group = = organic compounds (those which include carbon).
- Hydroxyl . -HE. The OH group of compounds of organic and inorganic types. The bond between oxygen and hydrogen atoms is covalent.
Carbonyl and hydroxyl have a mutual effect. What exactly determines the acid properties of the considered compounds? The fact that the polarization of the O – H bond causes an electron density shift to carbonyl oxygen.
It should be noted that in aqueous solutions, the substances of the carboxyl group dissociate (decompose) into ions. It looks like this: R-COOH = R-COO - + H + . By the way, the high boiling points of acids and their ability to dissolve in water are caused by the formation of hydrogen intermolecular bonds.
Dissociation
This is one of the properties of dicarboxylic acids, manifested in the decomposition of a substance into ions upon dissolution. It occurs in two stages:
- NOOS-X-COOH → NOOS-X-COO - + H + . In the first stage, dicarboxylic acids are stronger than monocarboxylic. Reason No. 1 is a statistical factor. There are 2 carboxyl groups in the molecule. Reason number 2 is their mutual influence. Which occurs in most cases, since the groups are either connected by a chain of multiple bonds, or are located nearby.
- NOOS-X-SOO - → - OOS-X-SOO - + H + . But in the second stage, the acids of this group become weaker than monocarboxylic. Except maybe ethandium (oxalic). The hydrogen cation is separated more difficult. This requires more energy. H + is more difficult to separate from the anion with a -2 charge than from -1.
Dissociation of dicarboxylic acids occurs only in aqueous solutions, although also in other cases, this chemical process is possible during melting.
Other reactions
The subject compounds may form salts. And not ordinary, like monocarboxylic, but acidic. They are characterized by the presence of two types of cations in the composition - metal (in some reactions, ammonium ions instead of them) and hydrogen. They also have a multiply charged anion of the acid residue - a negatively charged atom.
The name of these salts is due to the fact that upon hydrolysis they give an acidic reaction of the medium. It is worth noting that these compounds dissociate into a residue with a hydrogen particle and metal ions.
The chemical properties of dicarboxylic acids also determine their ability to form halides. In these compounds, the hydroxyl group is replaced by halogen, an energetic oxidizing agent.
Features
It is impossible not to make a reservation that the formation of chelates also belongs to the properties of dicarboxylic acids. These are complex compounds consisting of cyclic groups with a complexing agent (central ion).
Chelates are used to separate, analytically identify and concentrate a wide variety of elements. And in agriculture and medicine, they are used to enter trace elements such as manganese, iron, copper, etc.
Still some dicarboxylic acids form cyclic anhydrides - compounds R 1 CO-O-COR 2 , which are acylating agents that have the ability to react with nucleophiles, electron-rich chemicals.
And the last feature of dicarboxylic acids is the formation by them of polymers (high molecular weight substances). It occurs due to a reaction with other polyfunctional compounds.
Production methods
There are many of them, and each of them is aimed at the synthesis of a certain type of dicarboxylic acid. But there are several common ways:
- Oxidation of ketones - organic compounds with a carbonyl group = CO.
- Hydrolysis of nitriles. That is, the decomposition of organic compounds with the formula R — C≡N by means of water. Nitriles, as a rule, are solid or liquid substances with excellent solubility.
- Carbonylation of diols - substances with two hydroxyl groups. The reaction involves the introduction of C = O carbonyl groups by reaction with carbon monoxide, a very toxic gas that is lighter than air and has no smell or taste.
- Oxidation of diols.
Any of these methods will result in dicarboxylic acids. Of which there are a lot in nature. The names of most of them are well known to everyone, therefore it is also worth briefly telling about them.
Types of acids
The first thing to note is that they all have two names:
- Systematic . Given by the name of alkane (acyclic hydrocarbon) with the addition of the suffix "-dioia."
- Trivial . Given by the name of the natural product from which the acid is derived.
And now directly on the connections. So, here are some of the most famous acids:
- Oxal / ethandium. NOOS-COOH. Contained in carambol, rhubarb, sorrel. Also exists in the form of oxalates (salts and esters) of calcium and potassium.
- Malonic / propanedium. NOOS-CH 2 -COOH. Contained in sugar beet juice.
- Amber / Butanediol. NOOS- (CH 2 ) 2 -COOH. It looks like colorless crystals, perfectly soluble in alcohol and water. Contained in amber and in most plants. Salts and esters of this type of dicarboxylic acid are called succinates.
- Glutaric / Pentandiic. HOOC— (CH 2 ) 3 —COOH. Obtained by cyclic ketone oxidation with nitric acid and the participation of vanadium oxide.
- Adipic / Hexandium. NOOS (CH 2 ) 4 COOH. Obtained by the oxidation of cyclohexane in two stages.
In addition to the above, there is also heptandioic acid, nonanedioic, decandioic, undecandioic, dodecandioic, tridecandioic, hexadecandioic, geneicosanedioic and many others.
Aromatic Dicarboxylic Acids
A couple of words should be said about them too. Phthalic acids are the most important representative of this group. They are not industrially significant product, but are of interest. Since they are formed due to the production of phthalic anhydride - a substance by which dyes, resins and some components of drugs are synthesized.
Still there is terafl acid. It, interacting with alcohols, gives esters - derivatives of oxoacids. It is actively used in industry. Using terafl acid, saturated polyesters are obtained. And they are involved in the production of food containers, films for video, photo, audio recordings, bottles for drinks, etc.
It should be noted attention and isophthalic aromatic acid. It is used as a comonomer, a low molecular weight substance that forms a polymer due to the polymerization reaction. This property is used in the manufacture of rubber and plastic. And also insulating materials are made from it.
Application
This is the last thing. If we talk about the use of dibasic carboxylic acids, then it is worth noting that:
- They are the starting material with which halides, ketones, vinyl esters and other important organic compounds are obtained.
- Certain acids are involved in the production of esters, which are subsequently used in perfumes, textiles, and leather.
- Some of them are contained in preservatives and solvents.
- Without them, the production of kapron, a synthetic polyamide fiber, is not complete.
- Some acids are also used in the manufacture of thermoplastics called polyethylene terephthalate.
However, these are just some of the areas. There are many other areas in which specific types of dibasic acids are used. Oxal, for example, is used as a mordant in industry. Or as a precipitant of metal coatings. Suberinova is involved in the synthesis of drugs. Azelaic is used to make polyesters used in the manufacture of oil-resistant electrical cords, hoses and pipelines. So, if you think about it, there are very few areas where dibasic acids would not find their application.