Acids

Acids, a group of substances that are physically very different but possess characteristic chemical properties. The initial opinion of Lavoisier that the presence of O_a is characteristic of acids was long ago changed after the discovery of oxygen-free acids (HCN - Berthollet, 1787; HCl - Davy, 1810). The nomenclature of acids is mostly derived from that element or complex of elements which, excluding hydrogen (and oxygen), enters into their composition (for example, nitric, sulfuric, carbonic, ethyl-sulfuric); sometimes the designations are conventional: hydrochloric, formic, saccharic, etc. When a given element forms several acids with different numbers of oxygen atoms, the acid with the smallest number of oxygen atoms is designated -ous, with the largest -ic; intermediates are -ate, -ite (for example: HClO - hypochlorous; HClO₂ - chlorous; HClO₃ - chloric; HClO₄ - perchloric). The characteristic chemical properties of acids are their sour taste, their ability to turn blue vegetable matter - litmus - red, and the presence in the acid molecule of one or more hydrogen atoms capable of exchanging with a metal to form a salt. Since the theory of electrolytic dissociation (or "ionization" - Clausius; 1857), developed especially by Arrhenius (Arrhenius; 1884) and other outstanding physical chemists (Ostwald, Van't Hoff, Nernst), acids have been defined as compounds whose aqueous solutions contain hydrogen ions. The properties mentioned above and all other properties of acids are explained by the presence of hydrogen cations (H+) in the given solution (see Active reaction, Buffer properties). Acids are distinguished as mono- and polybasic. In monobasic acids, only one hydrogen atom in the acid molecule is capable of passing into ionic form; example: HCl → H+ + Cl'; in polybasic acids, several hydrogen atoms in the acid molecule are ionogenically bound; example: H₂SO₄; in this case, the ionization of polybasic acids occurs gradually depending on the concentration of the solution; thus, in concentrated solutions of H₂SO₄ it dissociates into H' and HSO₄' ions, i.e., H₂SO₄ → H' + HSO₄'; as further dilution with water begins, the ionization of the HSO₄' anion occurs → H' + SO₄', and only in very dilute solutions is almost complete absence of HSO₄' ions and almost complete ionization of H₂SO₄ → 2H' + SO₄' observed. The ability of acids to exchange hydrogen for metal according to the theory of electrolytic dissociation is manifested, for example, for zinc and sulfuric acid according to the equation: Zn + 2H' + SO₄' → Zn' + SO₄' + H₂, i.e., zinc is converted to the zinc ion by two hydrogen ions with the release of a hydrogen particle (not ionized). The characteristic property of acids to form salts with bases is expressed, for example, for HCl and caustic soda by the equation: H' + Cl' + Na' + OH' → Na' + Cl' + H₂O, i.e., the hydrogen and hydroxyl ions lose their electrical charges and form water. The strength of acids is proportional to the degree of their electrolytic dissociation, resp. ionization; the more molecules of a given acid at the same dilution dissociate into ions, the "stronger" it is; thus, for example, it has been established that the stronger hydrochloric acid at a concentration of 1 gram-molecule ("mole") per 1 liter dissociates almost completely into ions, while the weaker acetic acid is ionized under these conditions only by 2.4% (Thorns). The true ("active") acidity of a given solution is proportional to the concentration of hydrogen ions present in it. The acidity of a given solution, determined by the usual method of titration - titrable ("potential") acidity - is not a measure of "active", "true" acidity, because as titration proceeds, the binding of free hydrogen ions, their formation from as yet undissociated acid particles occurs. In other words, the usual titration methods determine the total ("total") acidity, equal to active + potential. Therefore, other research methods proved necessary for judging the active acidity of a given solution; the most important of these are: the electrometric method, the indicator method (see), the method of inversion of cane sugar and saponification of complex esters (based on the principle of the accelerating influence of hydrogen ions on the course of these processes). For illustration, a short comparative table of the strength of some acids (proportional to the concentration of H' ions), measured by the method of inversion and saponification on the one hand (a), and by the method of electrical conductivity on the other (b), is given. The strength of HCl is conventionally taken as 100 (Macleod). Acids a b 100 27 4.8 1.6 0.40 100 25 4.7 1.7 0.42 The difference in the strength of acids is manifested mainly in concentrated solutions; in this case, "weak" acids are very little dissociated into ions. As the solution is diluted, the degree of dissociation increases, and the difference in the strength of acids gradually begins to level out (see Electrolytic dissociation). Acetic acid when diluted from 1 mole to 32 liters is dissociated by 2.4%; to 128 liters - by 4.7%; to 512 liters - by 9.1%. The strongest among monobasic inorganic acids are hydrochloric, hydrobromic, hydroiodic, nitric, perchloric; among organic acids, strong ones are sulfonic; among dibasic, the strongest is sulfuric. The degree of ionization (dissociation) of a tenth-normal solution of nitric acid is 0.93, hydrochloric - 0.93, perchloric - 0.90, sulfuric - 0.62, carbonic - 0.0017.

M. Gramein. Organic acids. Among them, carboxylic acids occupy the first place, representing the final product of oxidation of primary alcohols: R.CH2(OH) (primary alcohol) → R.CH:O (aldehyde) → R.C(OH):O (acid). Upon dry distillation of their salts with sodium hydroxide, hydrocarbons and sodium carbonate (soda) are obtained; e.g., CH3.C(ONa):O + NaOH = CH4 (methane) + H2O.CO.ONa (soda). This indicates that carboxylic acids represent carbonic acid H2CO3, in which one hydroxyl is replaced by a hydrocarbon residue (radical): R.CO.OH. On the other hand, carboxylic acids can be considered as hydrocarbons in which a hydrogen atom is replaced by a residue of carbonic acid COOH, carboxyl. Depending on the number of carboxyl groups, monobasic acids R'.CO.OH, dibasic acids R"(CO.OH)2, etc. are distinguished. The radicals (R', R" etc.) may represent residues of saturated, unsaturated, cyclic, etc. hydrocarbons. The structure of the radicals determines the isomerism of acids. Acids derived from hydrocarbons with an open chain (acyclic hydrocarbons) are often called fatty acids, since many of them participate in the structure of fats, e.g., butyric acid CH3(CH2)2COOH, caproic acid CH3(CH2)4COOH, caprylic acid CH3(CH2)6COOH, capric acid CH3(CH2)8COOH, myristic acid CH3(CH2)12COOH, palmitic acid CH3(CH2)14COOH, stearic acid CH3(CH2)16COOH, etc., as well as unsaturated acids—oleic acid CH3(CH2)7CH:CH(CH2)7COOH, linoleic acid C18H32O2, linolenic acid C18H30O2, etc. Most carboxylic acids have empirical names determined by their origin or properties. Thus, the first acid—formic (H.COOH)—was first found in ants, the second (CH3.COOH)—acetic—in vinegar, etc. According to the international Geneva nomenclature, acids are named after the hydrocarbons in which hydrogen atoms are replaced by carboxyl groups; thus, CH3.COOH—acetic acid—is called methane-carboxylic acid; CH2:CH.COOH—ethylene-carboxylic acid, etc. Carboxylic acids are found in nature sometimes in the free state and in the form of salts, but mainly in the form of esters (see Esters). Esters of higher fatty acids and monohydric alcohols form wax (see) and spermaceti. Esters formed with trihydric alcohol—glycerol C3H6(OH)3—are called fats and oils. Fatty acids are a normal constituent of organisms; they are often formed in the processes of fermentation (acetic, butyric, etc.): acetic acid with traces of its homologs is obtained upon dry distillation of wood. Complete oxidation of primary alcohols gives corresponding acids. Into hydrocarbons through their halo derivatives, carboxyl can be introduced: 1) RCl + KCN → R.CN + KCl; R.CN + 3H2O → R.C(OH)3 + NH3; R.C(OH)3 → H2O + R.CO.OH; 2) RCl + Mg (in the presence of ether) → R.MgCl; R.MgCl + CO2 → R.CO.OMgCl; R.CO.OMgCl + H2O → R.CO.OH + Mg(OH)Cl. There exist many other methods for obtaining carboxylic acids, e.g., from three halogen derivatives: R.CCl3 + 3H2O → R.C(OH)3 + 3HCl; R.C(OH)3 → H2O + R.CO.OH. The chemical properties of carboxylic acids (R.CO.OH) are determined by the carboxyl and the radical. Upon dissolution in water, the hydrogen of the carboxyl passes into hydrogen ion (R.CO.OH ⇌ H+ + R.CO.O-), causing the reddening of blue litmus and the change of other indicators to hydrogen ion and the sensation of 'acid' taste. The hydrogen of the carboxyl can be replaced by metals, forming salts, by radicals of alcohols forming esters (R'CO.OR"). The hydroxyl of the carboxyl, upon the action of phosphorus halogen compounds, can be replaced by halogen (R.CO.Cl, R.CO.Br, etc.), giving halogen anhydrides (see). The hydroxyl of the acid can be replaced by the residue of ammonia—amides of acids are obtained (R.CO.NH2), by the residue of hydrazine (e.g., phenylhydrazine C6H5.NH.NH2)—hydrazides of acids (R.CO.NH.NH.C6H5). Upon the action of nitrous acid on hydrazides of acids, azides of acids (R.CO.N3) are formed, crystalline explosive substances. Anhydrides of monobasic carboxylic acids (RCO)2O cannot be obtained by simple removal of water from the acid, but are easily obtained by the action of salts of the acid on halogen anhydrides: R.CO.Cl + R.CO.ONa → NaCl + (R.CO)2O. Hydrogen atoms in the radical, the residue of hydrocarbons, can be replaced by halogens, giving halo-acids (e.g., chloroacetic acid CH2Cl.COOH). From the latter, by replacing the halogen with hydroxyl, alcohol-acids or oxycids [R"(OH).CO.OH], with the residue of ammonia (NH2)—amino-acids [R"(NH2).CO.OH], etc. are obtained. The entry of oxygen into the radical in the form of a carbonyl bond gives aldehyde- and ketone-acids (e.g., acetoacetic acid CH3.CO.CH2.COOH). Carboxylic acids having not more than ten carbon atoms are volatile with steam (which is used for their separation, purification, and identification) and are called volatile fatty acids. Often for the separation and characterization of acids, their calcium, magnesium, lead, or silver salts are used. Just as carboxylic acids are derived from carbonic acid, organic acids can be formed from other polybasic inorganic acids. Thus, from sulfuric acid (HO.SO2.OH), sulfonic acids (sulfocarboxylic acids) R.SO2.OH are derived. In them, sulfur is directly bound to carbon (e.g., CH3-SO2.OH). Isomeric with them are the sulfuric esters of acids, e.g., R.O.SO.OH. In some cases, sulfonic acids are obtained by the direct action of fuming sulfuric acid on open-chain hydrocarbons (on paraffins containing 6 to 8 carbon atoms); for obtaining sulfocarboxylic acids from hydrocarbons of the benzene series, this is a general method. Acyclic sulfonic acids are obtained by oxidation of mercaptans (thio-alcohols) R.SH + 3O → R.SO3H. Alkali salts of acyclic sulfonic acids are obtained by the action of haloalkyls on alkali salts of sulfurous acid (sulfites) RCl + Na2SO3 → NaCl + R.SO3Na. Sulfocarboxylic acids represent very 'strong' acids. Upon boiling with alkalis and acids, acyclic sulfocarboxylic acids do not change. Benzene sulfocarboxylic acids, when heated with acids (often under pressure), regenerate into benzene hydrocarbons, e.g., C6H5.SO3H + H2O → H2SO4 + C6H6. This can serve for the isolation, separation, and purification of benzene hydrocarbons. Salts of benzene sulfocarboxylic acids, when fused with alkalis, give salts of phenols, e.g., C6H5.SO3Na + 2NaOH → C6H5.ONa + Na2SO3 + H2O. This reaction has great technical importance. It is interesting that the introduction of a sulfogroup into benzene derivatives (similar to the introduction of a carboxyl group) reduces their toxicity; e.g., the highly toxic aniline (C6H5.NH2) gives sulfanilic acid C6H4(NH2)(SO3H), which is relatively less active on the organism; the same is the case when guaiacol C6H4(OH)(OCH3) passes into the potassium salt of the sulfonic acid—thioguaiacol C6H3(OH)(OCH3)(SO3K). From derivatives of acyclic sulfocarboxylic acids, biologically important is taurine (1,2-amino-ethane-sulfonic acid, NH2.CH2.CH2.SO3H). The product of reduction of aromatic (benzene) sulfocarboxylic acids (their chloranhydrides) are sulfinic acids, R.SO2H, which have very strong irritating properties with respect to the skin (they cause eczema in workers handling them). Derivatives of arsenic acid are kakodylic acid (Acidum kakodylicum), dimethyl-arsinic acid (CH3)2AsO(OH). Its sodium salt (Natrium kakodylicum) is a medicinal preparation. The sodium salt of methyl-arsinic acid—arrhenal (Arrhenalum) CH3.AsO(ONa)2—is also a medicinal preparation. From arsenic acid, aromatic derivatives are also important. Such is for example atoxyl (see).

A. Stepanov. Action of Acids on the Organism. The strength and depth of the local action of acids on protoplasm depend to a large extent on the indicated physicochemical properties. Concentrated acids attract water, bind all alkalis, displace weaker acids, and precipitate protein; this is the basis of their cauterizing action and destruction of tissue with the formation of more or less deep defects. Under the influence of diluted acids, connective tissue fibers loosen and swell. The antiseptic action of acids manifests naturally if they are highly concentrated and destroy protoplasm directly. But even diluted acids act antiseptically by removing water, precipitating proteins, and changing the necessary alkaline reaction for living protoplasm to acidic. For local cauterizing action, nitric, trichloroacetic, and lactic acids are most suitable, as their action can be more localized and delimited. For sensitive nerves, acids serve as strong irritants. A living cell is little permeable to most (not too concentrated) acids; when the cell dies, permeability increases. Smooth and striated muscle, under the influence of acids, as a rule, gives relaxation of tone; the tone of small vessels decreases. Muscle rigidity is more sharply expressed. When taken orally, diluted acids cause a feeling of roughness due to their action on the calcium salts of teeth. In the stomach, especially when the normal acidity of gastric juice is reduced, introduced acids (especially HCl) can improve gastric digestion and play the role of a disinfecting agent; moreover, under the influence of acids, the formation of secretin, pancreatic juice, and bile increases; in the lower parts of the small intestine, where the reaction is usually alkaline, acids act as a strong irritant and cause diarrhea. Prolonged excessive consumption of diluted acids impairs appetite and digestion and leads to a decline in nutrition. The fate of inorganic acids in the body differs from that of organic acids in that most of the latter, after absorption, burn to carbonates and, combining with alkalis, give alkaline-reacting compounds; therefore, the action of organic acids as such manifests mainly locally, before absorption. The main cases of therapeutic application of acids. Hydrochloric acid is prescribed for a deficiency of hydrochloric acid in the stomach; in some cases of increased acidity in the stomach, if it depends on the presence of fatty acids with increased fermentation processes. Hydrochloric acid (sometimes lactic acid) is often usefully prescribed for diarrhea in children, mainly on the basis of dyspepsia; the role of acids in this case is to improve gastric digestion and increase the tone of the pyloric part of the stomach, which promotes better processing of food in it. In febrile diseases, the application is still largely empirical, if we do not count the favorable effect on gastric dyspepsia; most commonly used are phosphoric, hydrochloric, and citric acids or various fruit lemonades. For local bleeding, acids are beneficial as hemostatic; for internal bleeding, the use of acids is still largely empirical. In poisoning with caustic alkalis, citric and acetic acids are most appropriate. Local external application of acids: for cauterization in infected wounds, small warts, calluses; in lupus; in the latter case, lactic acid was most commonly used, in the first-nitric and trichloroacetic. Rinsing with diluted acetic acid is recommended to reduce sweating; formic acid in the form of formic alcohol is used in chronic rheumatism and neuralgia.

M. Gramenitsky. Poisoning by acids. The action of acids on the organism depends on their concentration and chemical composition. In a toxicological sense, this is reflected in the predominance of local or general poisoning phenomena. Thus, with concentrated mineral acids (sulfuric, hydrochloric, nitric, phosphoric) and some organic (acetic), their local action is most sharply and primarily manifested, and only then does the general effect become apparent; the same acids in a diluted state give symptoms of general health disturbance without significant local action. Other acids (carbolic, oxalic, salicylic) along with the local tissue reaction to their action quickly give signs of general poisoning of the organism. In poisoning by boric and hydrocyanic acids, the main lesions are observed in the nervous system, as well as generally in tissues and organs not subjected to the direct action of the acids; local changes in such cases are insignificant or completely absent. Concentrated mineral and some organic acids at the site of application cause varying degrees of cauterization and sharp inflammatory phenomena; these acids decompose most salts and organic compounds; proteins coagulate, precipitate, which causes tissue necrosis (coagulation necrosis). Highly concentrated acids, especially sulfuric, have the property of taking up water and increasing their temperature when water is added; nitric and chromic acids act in an oxidizing manner. Symptoms of poisoning when concentrated mineral and organic (acetic, oxalic, salicylic, carbolic) acids are introduced orally appear very soon after their ingestion. A sharp sour taste is felt; burning pain in the mouth, esophagus, and stomach; severe vomiting is observed; very often coughing, partly due to the acid entering the upper respiratory tract, partly reflexively. When vomiting, bloody brown masses with a sharply acidic reaction are expelled; they have characteristics depending on the acid taken; thus, in poisoning with strong HCl, the vomit may sometimes be greenish in color; in poisoning with nitric acid, a yellowish flocculent admixture is observed in it; some acids give the vomit a specific odor (e.g., acetic, carbolic acid). Swallowing is difficult, sometimes completely impossible; breathing is difficult, the pulse is small and frequent, severe thirst. The excretion of feces and urine is delayed at the beginning of poisoning with mineral acids. Consciousness is preserved, but in poisoning by rapidly absorbed acids (carbolic, oxalic, hydrocyanic), along with other symptoms of nervous system damage, depression of consciousness, and often loss of consciousness, occurs very quickly. In poisoning with strong acids, a rapid decline in strength is observed. In cases of poisoning with these acids, death can occur very quickly: from asphyxiation due to edema of the larynx, from shock, internal bleeding; but most poisoned people die within the first day. The poison is removed from the body by vomiting, excreted by the kidneys, the gastric mucous membrane, saliva, and lungs (in poisoning by carbolic and acetic acids). If death does not occur in the first days after poisoning, then fever appears in the poisoned person, swelling and infiltration of the affected parts occur, intercostal and abdominal neuralgia are detected, albuminuria, cylinders, and blood elements are found in the urine. From the subsequent formation of scars at the site of action of the acid, strictures are possible, especially in the esophagus behind the larynx and above the entrance to the stomach, and in the stomach at its exit. - The course and outcome of poisonings depend on the degree of concentration and amount of acid taken, as well as whether the acid was taken on an empty or full stomach, how much acid remained in the stomach after vomiting, how quickly medical assistance was provided and what its nature was. In the treatment of acid poisoning, it is necessary to prescribe antidotes as soon as possible, which must have alkaline properties. Diluted acids, especially mineral ones, cause a sour taste in the mouth. Sulfuric acid quickly destroys the cement and dentin of teeth; nitric and hydrochloric acids quickly destroy tooth enamel and gradually destroy dentin. When entering the stomach, diluted acids cause significant secretion of pepsin. According to Yavorsky, the stomach easily tolerates large amounts of diluted acid (up to 500 cm³ of decinormal solution) without any harm to it or with minor disturbances. Poisoning by diluted acids causes disturbance of cardiac activity and respiration. Large doses of highly diluted acids cause pain in the stomach, colic, and diarrhea. Prolonged introduction of diluted mineral acids into the body disrupts digestion, blood formation, and nutrition. Some of the acids, when excreted from the body in the kidneys, become free, which explains the increase in urine acidity in carnivorous animals, the decrease in urine alkalinity or the transition of its reaction to acidic in herbivorous animals. Prolonged introduction of diluted acids into the body or intake of toxic amounts of them causes the removal of alkalis from the blood. What has been said about the action of diluted acids applies primarily to mineral and acetic acids; in poisoning by oxalic acid, nervous phenomena come to the forefront. - When acting on the skin, acids in a sufficient degree of concentration, especially sulfuric, their cauterizing action is detected. When sulfuric acid is poured on the skin, it first turns pale, then takes on a grayish color; later, on areas of skin destruction, constricting scars form. Other mineral acids have a similar action. Introduction of acids under the skin, even diluted, causes gangrene at the site of their injection. There are known cases of introduction of acids into the vagina and rectum for various reasons (with the aim of causing poisoning, producing an abortion, accidentally, etc.), where the corresponding local action of the acids is manifested, and also general action by absorption, especially in poisoning by carbolic acid. Patho-anatomical changes found in corpses in poisonings can only be summarized to a certain extent. Thus, one can note burns, necrosis of the mucous membrane of the digestive tract, their inflammatory condition when the above mineral and organic acids are introduced orally (except for hydrocyanic acid, in poisoning with pure preparations of which, for example, bitter almond water, the gastric mucosa does not show sharp changes). In prolonged cases of poisoning, degenerative changes in the heart, liver, kidneys are found upon autopsy; scar changes in tissues at the site of action of the acid. It should be noted that poisoning by one or another acid gives more or less typical for the action of this acid local, and in part general patho-anatomical changes. In poisoning by diluted mineral acids, the gastric mucosa may be unchanged, while traces of the corrosive action of the acid are found in the intestines. Mineral and some organic acids, as substances easily recognizable by their local cauterizing action on the oral mucous membrane, by taste, odor, and some (for example carbolic) also by color, cannot be a poison that can be easily introduced with criminal intent in a sufficient dose to poison another person without him noticing it. The latter does not apply to the highly toxic hydrocyanic acid or its preparations, which, as is known, can be given in food and drink and not be recognized by those who take them. However, a certain percentage of murders by poisoning with acids is known; this mostly applies to children and helpless persons, as well as to cases where the person taking the acid, due to deception, considers it a medicinal substance; it is possible to introduce acids into the vagina (during douching), into the rectum (in enemas) with criminal intent to poison. Mainly, however, poisonings by acids occur with the aim of suicide, accidentally, and so-called "medical" ones. The latter most of all applies to carbolic, salicylic, and boric acids. There are cases of intentional pouring of acids (mainly sulfuric) with the aim of disfigurement. At present, the most frequent poisonings are by acetic acid. Statistical data on poisoning by acids in the RSFSR are as follows. [Inorganic Organic poisons poisons Poisonings (ch and and and and s a> oa o» | With the aim of murder . . . Of the total number of murders - poisonings by acids . . . | With the aim of suicide . 48S Of the total number | of suicides - | poisonings by acids.. 1K1 | With the aim of infanticide . I Of the total number | of infanticides - | poisonings by acids.. a - - ! Accidents . . . V8 l.t93 | Of the total number of them - poisonings by acids..... There are known professional poisonings by acids, e.g., hydrocyanic acid (or its preparations) due to its use in electroplating, metallurgy, and for disinfection; sulfuric - due to the presence of acid vapors in the air during its production or where it is heated to the temperature of sulfuric anhydride release; nitric - during its manufacture, dissolution and etching of metals, during nitration of organic compounds, etc.; hydrochloric - due to the presence of hydrogen chloride vapors in the air of workrooms during its preparation; picric - when using it and its salts as explosives, from inhaling dust when filling shells, etc. These professional chronic poisonings by acids or their salts give more or less a specific picture of pathological changes in the body for each poisoning.]

V. Smolyaninov. For the treatment of acute poisoning with acids, burnt magnesia and soap water are used; chalk and soda—with caution, as the released CO₂ can lead to perforation of the stomach; mucous infusions and albumin water. Gastric lavage and emetics are contraindicated. In acute acidosis of the blood and tissues, the intravenous administration of alkaline solutions such as Ringer-Locke's solution is advisable.—LIST of acids used in medicine (FUP): Acidum aceticum, boricum, chromicum, hydrochloricum, lacticum, nitricum, phosphoricum, sulfuricum, tartaricum, trichloraceticum.