7440-47-3 Usage
Uses
1. Used in Automotive and Household Appliance Industry:
Chromium is used as a plating material for metal and plastic parts to produce a shiny, reflective finish. This application is particularly attractive in the automotive industry for automobile trim and in the household appliance industry for a polished look.
2. Used in Construction and Manufacturing Industry:
Chromium is used to make alloys, especially stainless steel, which is important for cookware and items that require strength and protection from rusting and high heat.
3. Used in Electrical Equipment Industry:
Its compounds are used for high-temperature electrical equipment due to their ability to withstand extreme temperatures.
4. Used in Leather Tanning Industry:
Chromium is used in the tanning of leather, where it helps to stabilize and preserve the leather.
5. Used in Textile Industry:
Chromium acts as a mordant, fixing the dyes in textiles so that they will not run, which is crucial for the textile industry.
6. Used in Paint Industry:
As an antichalking agent for paints, chromium helps to improve the durability and appearance of painted surfaces.
7. Used in Diagnostic Medicine:
Trace amounts of chromium are important for a healthy human diet, and its radioisotope, chromium-51, is used as a tracer to check the rate of blood flow in constricted arteries.
8. Used in Chemical Reactions:
Some chromium compounds, such as chromium chloride, chromic hydroxide, and chromic phosphate, are used as catalysts for organic chemical reactions.
9. Used in Gemstone and Laser Technology:
A small amount of chromium is responsible for the bright red color of the ruby gemstone and is used in the first ruby laser made from a ruby crystal of aluminum oxide (Al2O3).
10. Used in Steel Production:
Chromium is a key component in the production of steel, where it is added to improve mechanical properties, increase hardening, and enhance corrosion resistance.
11. Used in Refractory Furnaces:
Refractory bricks composed of oxides of magnesium, chromium, aluminum, and iron are used in the construction of furnaces and other high-temperature equipment.
12. Used in Decorative Electroplating:
Chromium coatings are applied on the surface of other metals for decorative purposes, to enhance resistance, and to lower the coefficient of friction.
Reactions
Chromium is oxidized readily in air forming a thin, adherent, transparent coating of Cr2O3.
Chromium forms both the chromous (Cr2+) and chromic (Cr3+) compounds that are highly colored.
Chromium metal reacts readily with dilute acids forming a blue Cr2+ (aq) solution with the evolution of hydrogen:
Cr + 2HCl → CrCl2 + H2
Chromium in metallic form and as Cr2+ ion are reducing agents. The Cr2+ reduces oxygen within minutes, forming violet Cr3+ ion:
4Cr2+(aq) + O2(g) + 4H+ (aq) → 4Cr3+ + 2H2O (l)
The standard redox potential for the overall reaction is 1.64V.
Cr3+ ion forms many stable complex ions. In the aqueous medium, it forms the violet Cr(H2O)63+ ion which is slightly basic. Chromium(III) ion is amphoteric, exhibiting both base and acid behavior.
Chromium reaction in an aqueous solution with a base produces a pale blue-violet precipitate having composition: Cr(H2O)3(OH)3.
Cr(H2O)63+ (aq) + 3OH– (aq) → Cr(H2O)3(OH)3 (s) + H2O
The above precipitate redissolves in excess base:
Cr(H2O)3(OH)3 (s) + H+ (aq) → Cr(H2O)4(OH)2+ (aq) + H2O
Chromium forms chromium(VI) oxide in which the metal is in +6 oxidation state. In acid medium it yields yellow chromate ion, CrO42–, and the redorange dichromate ion, Cr2O72–.
Chromium is oxidized in nitric, phosphoric or perchloric acid forming a thin oxide layer on its surface, thus making the metal even more unreactive to dilute acids.
Elemental chromium reacts with anhydrous halogens, hydrogen fluoride, and hydrogen chloride forming the corresponding chromium halides. At elevated temperatures in the range 600 to 700°C, chromium reacts with hydrogen sulfide or sulfur vapor, forming chromium sulfides.
Chromium metal reacts at 600 to 700°C with sulfur dioxide and caustic alkalis. It combines with phosphorus at 800°C. Reaction with ammonia at 850°C produces chromium nitride, CrN. Reaction with nitric oxide forms chromium nitride and chromium oxide.
5Cr + 3NO → 3CrN + Cr2O3
Production
Chromium metal is produced by thermal reduction of chromium(III) oxide, Cr2O3 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr2O3 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with Al powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen.
Cr2O3 + 2Al→ 2Cr + Al2O3
The carbon reduction process is carried out at 1,300 to 1,400°C at low pressure in a refractory reactor:
Cr2O3 + 3C→ 2Cr + 3CO
The silicon reduction process is not thermally self-sustaining and, therefore, is done in an electric arc furnace:
2Cr2O3 + 3Si → 4Cr + 3 SiO2
Chromium may be produced from high-carbon ferrochrome by electrolytic process. Alternatively, the metal may be obtained by electrolysis of chromic acid, H2CrO4.
High-carbon ferrochromium alloys are made by the reduction of chromite ore with carbon in an arc furnace. On the other hand, low-carbon ferrochromium is obtained by silicon reduction of the ore. The carbon content of ferrochromium can be reduced further by heating high-carbon alloys with ground quartzite or by oxidation in vacuum and removal of carbon monoxide formed. Ferrochromium alloys are used in the manufacture of stainless steel.
Toxicity
While chromium metal or trivalent chromium is not very toxic, hexavalent chromium (Cr6+) is carcinogenic and moderately toxic. Cr6+ is corrosive to skin and causes denaturation and precipitation of tissue proteins. Inhalation of Cr6+ dust or mist can cause perforation of the nasal septum, lung irritation, and congestion of the respiratory passsages. Chronic exposure may produce cancer of the respiratory tract.
Isotopes
There are 26 isotopes of the element chromium; four are stable and foundin nature, and the rest are artificially produced with half-lives from a few microsecondsto a few days. The four stable isotopes and their percentage of contribution to thetotal amount of chromium on Earth are as follows: 50Cr = 4.345%, 52Cr = 83.789%,53Cr = 9.501%, and 54Cr = 2.365%. Cr-50 is radioactive but has such a long halflife—1.8×10+17 years—that it is considered to contribute about 4% to the total amount ofchromium found on Earth.
Origin of Name
From the Greek word chroma or chromos, meaning “color,” because of
the many colors of its minerals and compounds.
Characteristics
Chromium is a hard, brittle metal that, with difficulty, can be forged, rolled, and drawn,unless it is in a very pure form, in which case the chromium is easier to work with. It is anexcellent alloying metal with iron. Its bright, silvery property makes it an appropriate metal toprovide a reflective, non-corrosive attractive finish for electroplating.Various compounds of chromium exhibit vivid colors, such as red, chrome green, andchromate yellow, all used as pigments.
History
Chromium was discovered in 1797 by Vauquelin, who prepared
the metal the next year, chromium is a steel-gray, lustrous,
hard metal that takes a high polish. The principal ore is chromite
(FeCr2O4), which is found in Zimbabwe, Russia, South
Africa, Turkey, Iran, Albania, Finland, Democratic Republic
of Madagascar, the Philippines, and elsewhere. The U.S. has
no appreciable chromite ore reserves. Chromium is usually
produced by reducing the oxide with aluminum. Chromium
is used to harden steel, to manufacture stainless steel, and to
form many useful alloys. Much is used in plating to produce
a hard, beautiful surface and to prevent corrosion. Chromium
is used to give glass an emerald green color. It finds wide
use as a catalyst. All compounds of chromium are colored;
the most important are the chromates of sodium and potassium
(K2CrO4) and the dichromates (K2Cr2O7) and the potassium
and ammonium chrome alums, as KCr(SO4)2·12H2O.
The dichromates are used as oxidizing agents in quantitative
analysis, also in tanning leather. Other compounds are of industrial
value; lead chromate is chrome yellow, a valued pigment.
Chromium compounds are used in the textile industry
as mordants, and by the aircraft and other industries for anodizing
aluminum. The refractory industry has found chromite
useful for forming bricks and shapes, as it has a high melting
point, moderate thermal expansion, and stability of crystalline
structure. Chromium is an essential trace element for human
health. Many chromium compounds, however, are acutely or
chronically toxic, and some are carcinogenic. They should be
handled with proper safeguards. Natural chromium contains
four isotopes. Twenty other isotopes are known. Chromium
metal (99.95%) costs about $1000/kg. Commercial grade
chromium (99%) costs about $75/kg.
Production Methods
Chromium metal is prepared by reducing the ore in a blast furnace with carbon (coke) or silicon to form an alloy of chromium and iron called ferrochrome, which is used as the starting material for the many iron-containing alloys that employ chromium. Chromium to be used in iron-free alloys is obtained by reduction or electrolysis of chromium compounds.Chromiumisdif?culttoworkinthepuremetalform; it is brittle at low temperatures, and its high melting point makes it dif?cult to cast.
Air & Water Reactions
May be pyrophoric, as dust. Insoluble in water.
Reactivity Profile
Chromium reacts violently with NH4NO3, N2O2, Li, NO, KClO3, SO2 . Metal dusts when suspended in atmospheres of carbon dioxide may ignite and explode.
Hazard
Hexavalent chromium compounds are
questionable carcinogens and corrosive on tissue,
resulting in ulcers and dermatitis on prolonged contact.
Hazard
Even though chromium may be a necessary trace element in our diets, many of its compounds are very toxic when ingested. Some are very explosive when shocked or heated (e.g., chromium nitrate) or when in contact with organic chemicals. Dust from the mining of chromium ores, which is found in igneous rocks, is carcinogenic and can cause lung cancer, even when small amounts are inhaled. Workers in industries that produce and use chromium are subject to bronchogenic cancer if precautions are not taken.
Health Hazard
The toxicity of chromium alloys and compoundsvaries significantly. Chromium metaldoes not exhibit toxicity. Divalent and trivalentcompounds of chromium have a loworder of toxicity. Exposure to the dusts ofchromite or ferrochrome alloys may causelung diseases, including pneumoconiosis andpulmonary fibrosis.Among all chromium compounds onlythe hexavalent salts are a prime health hazard.Cr6+ is more readily taken up bycells, than any other valence state of themetal. Occupational exposure to these compoundscan produce skin ulceration, dermatitis,perforation of the nasal septa, and kidneydamage. It can induce hypersensitivityreactions of the skin and renal tubular necrosis.Examples of hexavalent salts are thechromates and dichromates of sodium, potassium,and other metals. The water-solublehexavalent chromium salts are absorbed intothe bloodstream through inhalation. Manychromium(VI) compounds are carcinogenic,causing lung cancers in animals and humans.The carcinogenicity may be attributed tointracellular conversion of Cr6+ to Cr3+,which is biologically more active. The trivalentCr3+ ion can bind with nucleic acid andthus initiate carcinogenesis.Paustenbach et al. (1996) reported a casestudy on the uptake and elimination ofCr(VI) in drinking water on a male volunteerwho ingested 2 L/day of water containing2 mg/L Cr(VI) for 17 consecutivedays. The total chromium was measured inurine, plasma and red blood cells. The eliminationhalf-life in plasma was 36 hoursand the bioavailability was estimated as 2%.The steady-state chromium concentrations inurine and blood were achieved after sevendays of Cr(VI) ingestion. This study furthermorerevealed that Cr(VI) in drinkingwater at concentrations below 10 mg/L couldbe completely reduced to Cr(III) prior tosystemic distribution. In a follow-up study,Kergen et al. (1997) examined the magnitudeof absorption, distribution and excretionof Cr(VI) in drinking water in human volunteersfollowing oral exposures to singleand repeated doses at 5 and 10 mg Cr(VI)/L.The data obtained from this study indicatedthat virtually all (> 99.7%) of the ingestedCr(VI) was reduced to Cr(III) before enteringthe blood stream. No toxicity was observed.The endogenous reducing agents within theupper GI tract and the blood were attributedto reduce hexavalent chromium into its trivalentstate and, thus, prevented any systemicuptake of Cr(VI). Such reduction appearedto be effective even under the fasting conditions.Wise et al. (2002) investigated the cytotoxicityand clastogenicity of both water-insolubleand water-soluble Cr(VI) compounds in primaryhuman bronchial fibroblasts and foundthat they were overall cytotoxic and genotoxicto human lung cells. Although the genotoxicmechanisms of both may be mediated bysoluble Cr(VI) ions the water-insoluble saltsapparently are the potent carcinogens comparedto the water-soluble salts (Wise et al.2004). Exposure to Cr(VI) enhanced the bindingof polycyclic aromatic hydrocarbons toDNA in human lung cells (Feng et al. 2003).Hexavalent chromium has been found to besynergistic to benzo a pyrene diol epoxide onmutagenesis and cell transformation.The catalytic effect of iron on enhancingthe rate of reduction of Cr(VI) byhuman microsomes has been reported earlier(Myers and Myers 1998). Various formsof exogenous iron markedly enhanced bothliver and lung microsomal rates of Cr(VI)reduction. Small increases in intracellulariron have shown to cause large increases inin the rate and extent of Cr(VI) reduction.Thus, individuals exposed simultaneously toCr(VI) and agents that may increase intracellulariron could, therefore, be at potentiallygreater risk for toxicity and carcinogenicityof Cr(VI).
Fire Hazard
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.
Potential Exposure
Chromium metal is used in stainless and other alloy steels to impart resistance to corrosion, oxidation, and for greatly increasing the durability of metals; for chrome plating of other metals.
Veterinary Drugs and Treatments
Chromium supplementation may be useful in the adjunctive treatment
of diabetes mellitus or obesity, particularly in cats; there is
controversy whether this treatment is beneficial. It does not appear
to be useful in dogs with diabetes mellitus.
Carcinogenicity
Exposure to chromium compounds over a prolonged period has been observed in manyepidemiologicalstudiestoenhancetheriskofcancerof the respiratory organs among the exposed. The relationshipbetweenemploymentinindustriesproducingchromium compounds from chromite ore and enhanced risk of lungcancer iswell established.There isagreement inseveral studies that long-term exposure to some chromium-based pigments enhance the risk of lung cancer. An association has alsobeenobservedbetweenexposuretochromicacidinhard plating and lung cancer, but that association is not strong. Somestudieshaveweaklyindicatedexcessesofcancerofthe GItract,buttheresultsareinconsistentandarenotcon?rmed inwell-designedstudies.Thereisnoindicationthatchromite ore does have an associated enhanced risk of cancer. Although it has not yet been identi?ed which chromium compound (or compounds) is (are) responsible for enhanced risk of cancer in respiratory organs, there is general agreementthatitisthechromium(6+)speciesthatareresponsible for the elevated cancer risks and that the chromium species are not.
Environmental Fate
Chromium is distributed to the air, water, and soil from natural and anthropogenic sources. The environmental fate of chromium is dependent on the oxidation state and solubility of the compound and the environmental conditions affecting reduction or oxidation, such as pH. Oxidizing conditions favor the formation of Cr(VI) compounds, particularly at higher temperatures, while reducing conditions favor the formation of Cr(III) compounds. Chemical manufacturing and natural gas, oil, and gas combustion are the primary sources of chromium in the atmosphere.Most of the chromium in air eventually ends up in water or soil. Electroplating, textile manufacturing, cooling water, and leather tanning are major sources of chromium in wastewater discharges to surface waters. Chromium(III) is the predominant oxidation state of chromium in many soils. Cr(III) binds to soil and has low mobility. A lower soil pH favors the reduction of Cr(VI) to Cr(III). Runoff from soil and industrial processes may transport chromium to surface water.Cr(VI) compounds may leach into groundwater. The pH of the soil and aquatic environment is an important factor in chromium mobility, bioavailability, and toxicity. The chromate form predominates in most natural surface waters that are basic or neutral. The hydrochromate concentration increases in more acidic conditions.
Shipping
UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN1759 Corrosive solids, n.o.s., Hazard class: 8; Labels: 8-Corrosive material, Technical Name required
Toxicity evaluation
Chromium enters the air, water, and soil mostly in the chromium(
III) and chromium(VI) forms. In air, chromium
compounds are present mostly as fine dust particles, which
eventually settle over land and water. Chromium can strongly
attach to sediment and soil, and only a small amount is
expected to dissolve in water and leach though the soil to
groundwater. Fish do not accumulate much chromium in their
bodies.Most chromium exposure in the general population is
through ingestion of the chemical in food containing chromium(
II), although exposure is also possible as a result of
drinking contaminated well water, or living near uncontrolled
hazardous waste sites containing chromium or industries that
use chromium. Inhalation of chromium dust and skin contact
during use in the workplace are the main routes of occupational
exposure.
Incompatibilities
Dust may be pyrophoric in air. Chromium metal (especially in finely divided or powder form) and insoluble salts reacts violently with strong oxidants, such as hydrogen peroxide, causing fire and explosion hazard. Reacts with diluted hydrochloric and sulfuric acids. Incompatible with alkalis and alkali carbonates
Waste Disposal
Recovery and recycling is a viable alternative to disposal for chromium in plating wastes; tannery wastes; cooling tower blowdown water and chemical plant wastes.
Check Digit Verification of cas no
The CAS Registry Mumber 7440-47-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,4,4 and 0 respectively; the second part has 2 digits, 4 and 7 respectively.
Calculate Digit Verification of CAS Registry Number 7440-47:
(6*7)+(5*4)+(4*4)+(3*0)+(2*4)+(1*7)=93
93 % 10 = 3
So 7440-47-3 is a valid CAS Registry Number.
InChI:InChI=1/Cr
7440-47-3Relevant articles and documents
Kinetics and mechanism of chromium electrodeposition from formate and oxalate solutions of Cr(III) compounds
Protsenko,Danilov
, p. 5666 - 5672 (2009)
Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solu
Electrolytic preparation and characterization of VCr alloys in molten salt from vanadium slag
Liu, Shiyuan,Wang, Lijun,Chou, Kuo-chih,Kumar, Ramachandran Vasant
, p. 875 - 881 (2019)
Vanadium slag contains several critical elements like V, Ti, Cr, Fe and Mn. In our previous work, V and Cr have been enriched by selective chlorination, increasing from 10.05% to 14.95% and 5.84%–8.69% separately. V and Cr still maintain the trivalence state in molten salt. In the current work, the electrodeposition behaviors of V3+ and Cr3+ in NaCl–KCl molten salt at 800 °C were investigated using cyclic voltammetry (CV) and square wave voltammetry (SWV) with a tungsten electrode. It was found that the reduction processes of V3+ and Cr3+ consist of two steps, M3+/M2+, M2+/M. The diffusion coefficients of V3+ and Cr3+ in NaCl–KCl molten salt were measured by CV. The effect of VCl3/CrCl3 mass ratio on VCr alloy was investigated by a two-electrode under constant voltage. Pure Cr can be obtained at 2.8 V in the NaCl–KCl molten salt, while VCr alloy (3.71 mass % V-94.28 mass% Cr-2.01 mass % O) was obtained when electrolysis voltage was controlled to 2.8 V at 800 °C. The composition of VCr alloy can be designed by changing the molten salt composition. This method can be applied for direct preparation of VCr alloy from vanadium slag, thus offering the use of low cost raw materials with direct environmental benefits.
Powders of chromium and chromium carbides of different morphology and narrow size distribution
Loubiere,Laurent,Bonino,Rousset
, p. 935 - 944 (1998)
Powders of Cr and Cr carbides (Cr2C, Cr7C3, and Cr23C6) have been prepared by hydrogen reduction of CrO1.9 and Cr3C2 powders of different morphology, texture and specific surface area. The Cr and Cr carbides particles have the morphology of the parent compound and a narrow size distribution. Depending on the shape, the average size is of the order of some micrometers or some tens of micrometers. Starting with Cr3C2 allows the preparation of Cr powders at a temperature (1000 °C) markedly lower than that required when CrO1.9 is used as the precursor (1300 °C). However, a Cr3C2 specific surface area of the order of 10 m2/g is necessary to achieve this within a reasonably short time (6 to 12 h). Powders of the lower carbides are prepared by using a milder hydrogen thermal treatment.
Reactions of Cr atoms with NO, N2O, CO2, NO 2, and SO2 molecules
Smirnov,Akhmadov
, p. 617 - 623 (2010)
Experimental results on the interaction of Cr atoms with various oxygen-containing molecules (NO, N2O, CO2, NO2, and SO2) at high temperatures (>1000 K) are presented. It is demonstrated that activation barrier
Photoactivation of methyl acetate by chromium atoms
Billups,Bell, John P.,Hauge, Robert H.,Kline, Ellen S.,Wesley Moorehead,Margrave, John L.,McCormick, Fred B.
, p. 1917 - 1918 (1986)
Photolysis of the cocondensate of methyl acetate and chromium vapor yields a complex that decomposes to acetaldehyde and formaldehyde.
Fabrication and characterization of electrodeposited Co1-xCrx nanowires
Chaure,Coey
, p. 232 - 236 (2006)
Co1-xCrx alloy nanowires with 0.0 1 a porous alumina membrane from an electrolyte containing Co and Cr ions. The composition, structure and magnetic properties of the nanowires have been characterized. Cobalt-rich nanowires were electrodeposited at a potential of -1.0 V relative to Ag/AgCl and chromium-rich nanowires were deposited beyond -3.5 V. The optimized processing conditions include hydrogen annealing to give hysteresis loops for the Co80Cr20 nanowires with coercivity of up to 200 mT and squareness of up to 0.95. Magnetization of the Co80Cr20 nanowire is 77 A m2 kg-1 and the energy product of the arrays is 35 kJ m-3.
Valence-to-core X-ray emission spectroscopy identification of carbide compounds in nanocrystalline Cr coatings deposited from Cr(III) electrolytes containing organic substances
Safonov, Viktor A.,Vykhodtseva, Ludmila N.,Polukarov, Yurii M.,Safonova, Olga V.,Smolentsev, Grigory,Sikora, Marcin,Eeckhout, Sigrid G.,Glatzel, Pieter
, p. 23192 - 23196 (2006)
Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.
Thermal studies of chromium, molybdenum and ruthenium complexes of chloranilic acid
Soliman,Ali,Khalil,Ramadan
, p. 37 - 42 (2000)
Chromium, molybdenum and ruthenium complexes of chloranilic acid (H2CA) were investigated by the thermogravimetric (TG) technique. The TG plot of Cr(H2CA)3 showed three decompositions in the temperature range 336-802°K. On
Synthesis of monodisperse chromium nanoparticles from the thermolysis of a Fischer carbene complex
Son, Seung Uk,Jang, Youngjin,Yoon, Ki Youl,An, Changhua,Hwang, Yosun,Park, Je-Geun,Noh, Han-Jin,Kim, Jae-Young,Park, Jae-Hoon,Hyeon, Taeghwan
, p. 86 - 88 (2005)
We successfully synthesized monodisperse chromium nanoparticles from the thermolysis of a Fischer carbene complex.
Reactions of chromium atoms with chloromethanes
Zaslonko,Smirnov
, p. 444 - 446 (2000)
The rate constants of the gas-phase reactions of the chromium atom with CCl4, CHCl3, and CH2Cl2 were measured behind shock waves at 800-1400 K. The rate constants of hexacarbonyl decomposition and chromium atom yield agreed well. The rate of formation of chromium atoms was slightly lower than the rate of consumption of parent molecules. At > 800 K (lower-temperature boundary of the reactions of chromium atoms with chloromethanes), the yield of chromium atoms in the course of Cr(CO)6 thermal decomposition may be considered an instantaneous process, i.e., its characteristic time is much shorter than the characteristic resolution time of the optical system. The rate constants were determined via monitoring a decrease in the chromium atom concentration with time. The available thermochemical data on the detachment of the chlorine atom from studied chloromethanes and on the dissociation of CrCl molecules showed that the reactions with the participation of CCl4 and CHCl3 were probably exothermic. A more detailed theoretical treatment of the reactions studied was complicated by the absence of accurate thermochemical data, primarily for the dissociation energy of the Cr-Cl bond.
