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| Names | |||
|---|---|---|---|
| Other names Potassium chlorate(VII); Perchloric acid, potassium salt; peroidin | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.029.011 | ||
| EC Number |
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| RTECS number |
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| UNII | |||
| UN number | 1489 | ||
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| Properties | |||
| KClO4 | |||
| Molar mass | 138.55 g/mol | ||
| Appearance | colourless/ white crystalline powder | ||
| Density | 2.5239 g/cm3 | ||
| Melting point | 610 °C (1,130 °F; 883 K) decomposes from 400 °C[4][5] | ||
| 0.76 g/100 mL (0 °C) 1.5 g/100 mL (25 °C)[1] 4.76 g/100 mL (40 °C) 21.08 g/100 mL (100 °C)[2] | |||
Solubility product (Ksp) | 1.05·10−2[3] | ||
| Solubility | negligible inalcohol insoluble inether | ||
| Solubility inethanol | 47 mg/kg (0 °C) 120 mg/kg (25 °C)[2] | ||
| Solubility inacetone | 1.6 g/kg[2] | ||
| Solubility inethyl acetate | 15 mg/kg[2] | ||
Refractive index (nD) | 1.4724 | ||
| Structure | |||
| Rhombohedral | |||
| Thermochemistry | |||
| 111.35 J/mol·K[6] | |||
Std molar entropy(S⦵298) | 150.86 J/mol·K[6] | ||
Std enthalpy of formation(ΔfH⦵298) | −433 kJ/mol[7] | ||
Gibbs free energy(ΔfG⦵) | −300.4 kJ/mol[2] | ||
| Hazards | |||
| GHS labelling: | |||
  [5] | |||
| Danger | |||
| H271,H302,H335[5] | |||
| P220,P280[5] | |||
| NFPA 704 (fire diamond) | |||
| Safety data sheet (SDS) | MSDS | ||
| Related compounds | |||
Otheranions | Potassium chloride Potassium chlorate Potassium periodate | ||
Othercations | Ammonium perchlorate Sodium perchlorate | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Potassium perchlorate is the inorganicsalt with the chemical formulaKClO4. Like otherperchlorates, this salt is a strongoxidizer when the solid is heated at high temperature, although it usually reacts very slowly in solution with reducing agents or organic substances. This colorless crystalline solid is a common oxidizer used infireworks,ammunitionpercussion caps, andexplosive primers, and is used variously inpropellants,flash compositions, stars, andsparklers. It has been used as asolid rocket propellant, although in that application it has mostly been replaced by the more performantammonium perchlorate.
KClO4 has a relatively lowsolubility in water (1.5 g in 100 mL of water at 25 °C).[1]
Potassium perchlorate is prepared industrially by treating an aqueous solution ofsodium perchlorate withpotassium chloride. This single precipitation reaction exploits the lowsolubility of KClO4, which is about 1/100 as much as the solubility of NaClO4 (209.6 g/100 mL at 25 °C).[8]
It can also be produced by bubbling chlorine gas through a solution ofpotassium chlorate andpotassium hydroxide,[citation needed] and by the reaction ofperchloric acid with potassium hydroxide; however, this is not used widely due to the dangers of perchloric acid.
Another preparation involves theelectrolysis of a potassium chlorate solution, causing KClO4 to form and precipitate at theanode. This procedure is complicated by the low solubility of both potassium chlorate and potassium perchlorate, the latter of which may precipitate onto the electrodes and impede the current.
KClO4 is anoxidizer, greatly increasing the rate ofcombustion of combustible materials relative to burning in air. Combustion withglucose givescarbon dioxide, water molecules andpotassium chloride:
The conversion of solid glucose into hot gaseous CO2 is the basis of the explosive force of this and other such mixtures. Withsugar,KClO4 yields a low explosive, provided a necessary confinement. Otherwise such mixtures simplydeflagrate with an intense purple flame characteristic ofpotassium. Flash compositions used infirecrackers, defined in the US as containing 50 mg of powder or less, usually consist of a mixture ofaluminium powder and potassium perchlorate, although this is one of the few instances where potassium chlorate is still allowed as a major component.[9] This mixture, called flash powder, is also used in ground and airfireworks.
As an oxidizer, potassium perchlorate can be used safely in the presence ofsulfur, whereaspotassium chlorate cannot. The greater reactivity of chlorate is typical – perchlorates arekinetically poorer oxidants.Chlorate can producechloric acid (HClO3) in contact with impure acidic sulfur or certain sulfur compounds, which is highly unstable and can lead to premature ignition of the composition. Otherwise the sensitivity of perchlorate / sulfur mixtures is about the same as chlorate / sulfur mixtures, although it lowers the ignition temperature of chlorate mixtures more.[10] Correspondingly,perchloric acid (HClO4) is quite stable.[11][page needed]
In commercial use, potassium perchlorate is used in consumer and display pyrotechnics,[9][10]: 17–14 some types of solid rocket fuels,[12] and specialtyblack powder substitutes such as Pyrodex. The exact compositions for different types are trade secrets, but the SDS lists the components as:[13]
| Chemical | Percent Range |
|---|---|
| Potassium perchlorate | 15-40% |
| Potassium nitrate | 15-40% |
| Sodium benzoate | 5-10% |
| Sodium nitrate | 1-5% |
Depending on the specific mixture, it is classified as either 1.3C or 1.4C for shipping. The 1.4C designation of "no significant blast hazard" allows up to 75 kilograms (165 lb) to be shipped by air.[13]: 6
Potassium perchlorate can be used as anantithyroid agent used to treathyperthyroidism, usually in combination with one other medication. This application exploits the similarionic radius andhydrophilicity of perchlorate andiodide.
Perchlorate ion, a common low-level water contaminant in the USA due to theaerospace industry,[citation needed] has been shown to reduce iodine uptake and thus is classified as agoitrogen. Perchlorate ion is a competitive inhibitor of the process by which iodide is actively accumulated into the thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above7 μg/(kg·d), perchlorate begins to temporarily inhibit the thyroid gland's ability to absorb iodine from the bloodstream. This level is 9000 times greater than has been found in anywater supply, however.[14]
The reduction of the iodide pool by perchlorate has a dual effect – reduction of excesshormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis andhypothyroidism on the other. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.[15]
Treatment of hyperthyroidism (includingGraves' disease) with600–2000 mg potassium perchlorate (430–1400 mg perchlorate) daily for periods of several months, or longer, was once a common practice, particularly in Europe,[14][16] and perchlorate use at lower doses to treat thyroid problems continues to this day.[17] Although400 mg of potassium perchlorate divided into four or five daily doses was used initially and found effective, higher doses were introduced when400 mg/d was discovered not to control thyrotoxicosis in all subjects.[14][15]
Current regimens for treatment of hypothyroidism (including Graves' disease), when a patient is exposed to additional sources of iodine, commonly include500 mg potassium perchlorate twice per day for 18–40 days.[14][18]
In another related study were subjects drank just 1 litre (34 US fl oz) of perchlorate-containing water per day at a concentration of10 ppm, i.e. daily10 mg of perchlorate ions were ingested, an average 38% reduction in the uptake of Iodine was observed.[19]
However, when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately0.5 mg/(kg·d),[by whom?] as in the above paragraph, a 67% reduction of iodine uptake would be expected. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine.[20] This may well be attributable to sufficient daily exposure, or intake, of stableiodine-127 among these workers and the short 8 hrbiological half life of perchlorate in the body.[14][medical citation needed]
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