Dicarboxylic acids are substances with two functional monovalent carboxyl groups - COOH, whose function is to determine the basic properties of these substances.
Their general formula is HOOC-R-COOH. And here, "R" refers to any organic 2-valent radical, which is the atoms connected to the functional group of the molecule. However, you can learn more about this.
Physical properties
Dicarboxylic compounds are solids. The following physical properties can be distinguished:
- Excellently soluble in water. At the same time, hydrogen intermolecular bonds are formed.
- The solubility limit in H2O is in the limit C6-C7. And this is understandable, because the content of the carboxyl polar group in the molecules is significant.
- Poorly soluble in solventsorganic origin.
- Melted at much higher temperatures than alcohols and chlorides. This is due to the high strength of their hydrogen bonds.
- If carboxylic compounds are subjected to heat, 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 \u003d C \u003d O organic compounds (those that include carbon).
- Hydroxyl. -IS HE. The OH group of compounds of organic and inorganic types. The bond between oxygen and hydrogen atoms is covalent.
Carbonyl and hydroxyl have mutual influence. What exactly determines the acidic properties of the compounds under consideration? The fact that the polarization of the O-H bond causes a shift in electron density to carbonyl oxygen.
It is worth noting that in aqueous solutions 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 due to the formation of hydrogen intermolecular bonds.
Dissociation
This is one of the properties of dicarboxylic acids, which manifests itself in the decomposition of a substance into ions upon dissolution. Occurs in two stages:
- NOOS-X-COOH → NOOS-X-COO-+N+. For the first stagedicarboxylic acids are stronger than monocarboxylic acids. Reason 1 is a statistical factor. There are 2 carboxyl groups in the molecule. Reason number 2 - their mutual influence. Which happens in most cases, since the groups are either connected by a chain of multiple bonds, or are not far away.
- HOOS-X-SOO- → -OOS-X-SOO -+N+. But in the second stage, the acids of this group become weaker than monocarboxylic ones. Except perhaps for ethandioic (oxalic). The hydrogen cation is more difficult to separate. This requires more energy. H+ is more difficult to separate from an anion with -2 charge than from -1.
Dissociation of dicarboxylic acids occurs only in aqueous solutions, although in other cases this chemical process is also possible during melting.
Other reactions
The compounds under consideration can form s alts. And not ordinary, like monocarboxylic, but sour. They are characterized by the presence in the composition of two types of cations - metal (in some reactions, instead of them, ammonium ions) and hydrogen. They also have a multiply charged anion of the acid residue - a negatively charged atom.
The name of these s alts is due to the fact that during hydrolysis they give an acid reaction of the medium. It should be noted that these compounds dissociate into a residue with a hydrogen particle and metal ions.
Also, the chemical properties of dicarboxylic acids determine their ability to form acid halides. In these compounds, the hydroxyl group is replaced by a halogen, a vigorous 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 determine and concentrate a wide variety of elements. And in agriculture and medicine, they are used to introduce micronutrients such as manganese, iron, copper, etc. into food.
Some more dicarboxylic acids form cyclic anhydrides - compounds R1CO-O-COR2, which are acylating agents with the ability react with nucleophiles, electron-rich chemicals.
And the last feature of dicarboxylic acids is their formation of polymers (high molecular weight substances). It occurs as a result of a reaction with other polyfunctional compounds.
Methods of obtaining
There are many of them, and each of them is aimed at the synthesis of a certain type of dicarboxylic acid. But there are some 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 with water. Nitriles are generally solid or liquid substances with excellent solubility.
- Carbonylation of diols - substances with two hydroxyl groups. The reaction involves the introduction of C=O carbonyl groupsby reacting with carbon monoxide, a highly toxic gas that is lighter than air and has no smell or taste.
- Oxidation of diols.
Any of these methods will lead to the production of dicarboxylic acids. There are a lot of them in nature. Everyone knows the names of most of them, so it’s worth briefly talking about them too.
Types of acids
The first thing to note is that they all have two names:
- Systematic. It is given by the name of the alkane (acyclic hydrocarbon) with the addition of the suffix "-dioic".
- Trivial. Given by the name of the natural product from which the acid is obtained.
And now directly about connections. So, here are some of the most famous acids:
- Oxalic/ethandium. NOOS-COON. Contained in carambola, rhubarb, sorrel. Also exists as calcium and potassium oxalates (s alts and esters).
- Malon/propandium. NOOS-CH2-COOH. Found in sugar beet juice.
- Amber/Butane. HOOS-(CH2)2-COOH. It looks like colorless crystals, perfectly soluble in alcohol and water. Found in amber and in most plants. S alts and esters of this type of dicarboxylic acid are called succinates.
- Glutaric/Pentandioic. HOOC-(CH2)3-COOH. Obtained by the oxidation of a cyclic ketone with nitric acid and the participation of vaniadium oxide.
- Adipic/Hexandioic. NOOS(CH2)4COOH. receivethrough the oxidation of cyclohexane in two steps.
In addition to the above, there is also heptanedioic acid, nonanedioic, decandioic, undecanedioic, dodecanedioic, tridecandioic, hexadecandioic, heneicosandioic and many others.
Aromatic dicarboxylic acids
A few words should also be said about them. Phthalic acids are the most important representative of this group. They are not an industrially significant product, but they are of interest. Since they are formed as a result of the production of phthalic anhydride - a substance with which dyes, resins and some components of medicines are synthesized.
There is also teraphlic acid. It, interacting with alcohols, gives esters - derivatives of oxo acids. It is actively used in industry. With the help of teraflic acid, saturated polyesters are obtained. And they are used in the production of food containers, film 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 as a result of a polymerization reaction. This property is used in the production of rubber and plastic. It is also used to make insulating materials.
Application
A last word about this. If we talk about the use of dibasic carboxylic acids, then it is worth noting that:
- They are raw materials, usingwhich produce acid halides, ketones, vinyl ethers and other important organic compounds.
- Certain acids are involved in the production of esters, which are further used in perfumery, textile industry, leather business.
- Some of them are found in preservatives and solvents.
- The production of capron, a synthetic polyamide fiber, is indispensable without them.
- Some acids are also used in the manufacture of a thermoplastic called polyethylene terephthalate.
However, these are just some areas. There are many other areas in which specific types of dibasic acids are used. Oxalic, for example, is used as a mordant in industry. Or as a precipitator for metal coatings. Suberic is involved in the synthesis of drugs. Azelaic is used to make polyesters used in the production 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 use.
