Silicic acid

Silicic acid
Names
IUPAC name
Silicic acid
Other names
Monosilicic acid
Orthosilicic acid
Identifiers
10193-36-9 YesY
ChEBI CHEBI:26675 YesY
ChemSpider 14236 YesY
EC Number 233-477-0
2009
Jmol 3D image Interactive graph
PubChem 14942
Properties
H4O4Si
Molar mass 96.11 g·mol−1
Acidity (pKa) 9.84, 13.2
Related compounds
Related compounds
 Orthocarbonic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Silicic acid /sɪˈlɪsɪk ˌæsɪd/ is a chemical compound. Silicic acid is the general name for a family of chemical compounds containing the element silicon attached to oxide and hydroxyl groups. This family of compounds have the general formula [SiOx(OH)4-2x]n.[1][2] Some simple silicic acids have been identified, but only in very dilute aqueous solution, such as metasilicic acid (H2SiO3), orthosilicic acid (H4SiO4, pKa1=9.84, pKa2=13.2 at 25 °C), disilicic acid (H2Si2O5), and pyrosilicic acid (H6Si2O7); however in the solid state these probably condense to form polymeric silicic acids of complex structure.

Ball-and-stick model of the orthosilicic acid molecule
orthosilicic acid
Ball-and-stick model of the disilicic acid molecule
disilicic acid
Ball-and-stick model of the metasilicic acid molecule
metasilicic acid
Ball-and-stick model of the pyrosilicic acid molecule
pyrosilicic acid

Chemical reactions

In general, silicic acid reactions are difficult to control. Partial dehydration to metasilicic acid, for example, is challenging because the reaction typically progresses all the way to silicon dioxide and water.

Acid-base reactions

Like other silanols, silicic acid is a weak acid. It can be deprotonated in solution, the conjugate base silicate is known.

Production

Silicic acid was discovered by Jöns Jacob Berzelius between 1810 and 1836 when studying silicon generated by his experiments. However, he failed to recognise it as distinct from silicon dioxide.

Hydration

Naturally occurring silicic acid is produced by a non-biological process called hydration involving water, and quartz, which is known to be common on Earth. The reaction producing silicic acid from quartz can be written as: Quartz + Water → Silicic acid, or (in balanced form): SiO
2 + 2 H
2O → H
4SiO
4.

Laboratory synthesis

Silicic acid can be produced by the acidification of sodium silicate in aqueous solution. The main problem in using silicic acids in chemical synthesis is that silicic acids readily lose water to form randomly polymeric silica gel, a form of silicon dioxide. Such conversion involve condensations.

Oceanic silicic acid

2009 silicic acid concentration in the upper pelagic zone.[3]

Silicic acid is created near the ocean's surface, by the process of hydration. It is carried into the abyssopelagic zone by falling water in the poles. Uncontrolled build-up of silicic acid in the ocean is naturally checked – although human influence can upset this natural regulation. It is primarily removed by conversion to silicon dioxide and water. In the oceans, silicon exists primarily as orthosilicic acid (H4SiO4), and its biogeochemical cycle is regulated by the group of algae known as the diatoms.[4][5] These algae polymerise the silicic acid to so-called biogenic silica, used to construct their cell walls (called frustules).

Silicic acid in health

Continuing research of the correlation of aluminium and Alzheimer's disease has in the last few years included the use of silicic acid in beverages,[6][7][8] due to its abilities to both reduce aluminium uptake in the digestive system as well as cause renal excretion of aluminium.

Study has shown that physiological concentration of orthosilicic acid stimulates collagen type 1 synthesis and osteoblastic differentiation in human osteoblast-like cells in vitro.[9]

Choline-stabilized orthosilicic acid is a bioavailable nutritional supplement. It has been shown to prevent the loss of hair tensile strength,[10] have positive effect on skin surface and skin mechanical properties, and on brittleness of hair and nails,[11] abate brittle nail syndrome,[12] partially prevent femoral bone loss in the aged ovariectomized rat model,[13] increase collagen concentration in calves,[14] and have potential beneficial effect on bone collagen formation in osteopenic females.[15]

References

  1. ↑ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
  2. ↑ R. K. Iler, The Chemistry of Silica, Wiley, New York, 1979.
  3. ↑ http://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html
  4. ↑ Siever, R. (1991). Silica in the oceans: biological-geological interplay. In: Schneider, S. H., Boston, P. H. (eds.), Scientists On Gaia, The MIT Press, Cambridge MA, USA, pp. 287-295.
  5. ↑ Treguer, P., Nelson, D. M., Van Bennekom, A. J., DeMaster, D. J., Leynaert, A. and Queguiner, B. (1995). The silica balance in the world ocean: A reestimate. Science 268, 375-379.
  6. ↑ Exley C, Korchazhkina O, Job D, Strekopytov S, Polwart A, Crome P (2006). "Non-invasive therapy to reduce the body burden of aluminium in Alzheimer's disease". J. Alzheimers Dis. 10 (1): 17–24; discussion 29–31. PMID 16988476.
  7. ↑ González-Muñoz MJ, Peña A, Meseguer I (2008). "Role of beer as a possible protective factor in preventing Alzheimer's disease". Food Chem. Toxicol. 46 (1): 49–56. doi:10.1016/j.fct.2007.06.036. PMID 17697731.
  8. ↑ Gonzalez-Muñoz MJ, Meseguer I, Sanchez-Reus MI, et al. (2008). "Beer consumption reduces cerebral oxidation caused by aluminum toxicity by normalizing gene expression of tumor necrotic factor alpha and several antioxidant enzymes". Food Chem. Toxicol. 46 (3): 1111–8. doi:10.1016/j.fct.2007.11.006. PMID 18096288.
  9. ↑ Reffitt DM, Ogston N, Jugdaohsingh R, et al. (2003). "Orthosilicic acid stimulates collagen type 1 synthesis and osteoblastic differentiation in human osteoblast-like cells in vitro". Bone 32 (2): 127–35. doi:10.1016/S8756-3282(02)00950-X. PMID 12633784.
  10. ↑ Wickett RR, Kossmann E, Barel A, et al. (2007). "Effect of oral intake of choline-stabilized orthosilicic acid on hair tensile strength and morphology in women with fine hair". Arch. Dermatol. Res. 299 (10): 499–505. doi:10.1007/s00403-007-0796-z. PMID 17960402.
  11. ↑ Barel A, Calomme M, Timchenko A, et al. (2005). "Effect of oral intake of choline-stabilized orthosilicic acid on skin, nails and hair in women with photodamaged skin". Arch. Dermatol. Res. 297 (4): 147–53. doi:10.1007/s00403-005-0584-6. PMID 16205932.
  12. ↑ Scheinfeld N, Dahdah MJ, Scher R (2007). "Vitamins and minerals: their role in nail health and disease". J Drugs Dermatol 6 (8): 782–7. PMID 17763607.
  13. ↑ Calomme M, Geusens P, Demeester N, et al. (2006). "Partial prevention of long-term femoral bone loss in aged ovariectomized rats supplemented with choline-stabilized orthosilicic acid". Calcif. Tissue Int. 78 (4): 227–32. doi:10.1007/s00223-005-0288-0. PMID 16604283.
  14. ↑ Calomme MR, Vanden Berghe DA (1997). "Supplementation of calves with stabilized orthosilicic acid. Effect on the Si, Ca, Mg, and P concentrations in serum and the collagen concentration in skin and cartilage". Biol Trace Elem Res 56 (2): 153–65. doi:10.1007/BF02785389. PMID 9164661.
  15. ↑ Spector TD, Calomme MR, Anderson SH, et al. (2008). "Choline-stabilized orthosilicic acid supplementation as an adjunct to Calcium/Vitamin D3 stimulates markers of bone formation in osteopenic females: a randomized, placebo-controlled trial". BMC Musculoskelet Disord 9: 85. doi:10.1186/1471-2474-9-85. PMC 2442067. PMID 18547426.

External links

This article is issued from Wikipedia - version of the Monday, February 29, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.