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Orthosilicic acid
Chemical compound assumed present in dilute solutions of silicon dioxide in water

Orthosilicic acid is an inorganic compound with the formula Si(OH)4. Although rarely observed, it is the key compound of silica and silicates and the precursor to other silicic acids [H2xSiOx+2]n. Silicic acids play important roles in biomineralization and technology. It is the parent acid of the orthosilicate anion SiO4−4.

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Isolation

Typically orthosilicic acid is assumed to be a product of the hydrolysis of its esters, Si(OR)4, where R stands for organyl group, as is practiced in sol-gel syntheses.4 These conditions are however too vigorous to allow isolation of the parent acid.

Orthosilicic acid can be produced by Pd-catalyzed hydrogenolysis of tetrabenzoxysilicon:5

Si(OCH2Ph)4 + 4 H2 → Si(OH)4 + 4 PhCH3

The acid was crystallized from a solution of dimethylacetamide and tetrabutylammonium chloride. As established by X-ray crystallography, the chloride anions interact with the acid via hydrogen bonds. Otherwise, the structure consists of the expected tetrahedral silicon center.

Reactions

Silicic acid readily condenses to give "higher" silicic acids including disilicic (pyrosilicic) and cyclo-tetrasilicic acid, (−O−Si(OH)2−)4:6

2 Si(OH)4 → O(Si(OH)3)2 + H2O 4 Si(OH)4 → (−O−Si(OH)2−)4 + 4 H2O

These derivatives have also been characterized crystallographically.

Orthosilicic acid in plants

Silicon has been explored as a nutrient for plant growth, with silica constituting up to 10% of plant weight on a dry matter basis.7 Orthosilicic acid is of particular interest as it is thought to be the form in which plants acquire silicon from the soil,89 before being deposited as phytoliths throughout the plant, leading to research in the application of orthosilicic acid through foliar sprays to supplement plant growth.10 Studies have demonstrated that foliar application of stabilized orthosilicic acid can alleviate abiotic stressors such as drought,1112 heavy metal toxicity,1314 and salinity,15 resulting in increased yields.16 Additionally, applications of orthosilicic acid have been demonstrated to reduce fungal infections and disease in plants,17 suggesting the possibility of using stabilized orthosilicic acid as an alternative or complement to existing disease control measures. The mechanisms by which orthosilicic acid alleviates abiotic stress and controls diseases is not well understood; current theories advanced include the activation of plant defense reactions18 and the precipitation of silica in the apoplast of the plant.19

Oceanic silicic acid

Dissolved silica (DSi) is a term used in the field of oceanography to describe the form of water-soluble silica, which is assumed to be Si(OH)4 (orthosilicic acid) or its conjugate bases (orthosilicate anions) such as −O−Si(OH)3 and (−O−)2Si(OH)2. Theoretical computations indicate that the dissolution of silica in water proceeds through the formation of a SiO2·2H2O complex and then orthosilicic acid.20 The biogeochemical cycle of silica is regulated by the algae known as the diatoms.2122 These algae polymerise the silicic acid to so-called biogenic silica, used to construct their cell walls (called frustules).23

In the uppermost water column the surface ocean is undersaturated with respect to dissolved silica, except for the Antarctic Circumpolar Current south of 55°S.

The dissolved silica concentration increases with increasing water depth, and along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean.2425

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. Gerhard Lagaly; Werner Tufar; A. Minihan; A. Lovell (2007). "Silicates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a23_661. ISBN 978-3-527-30673-2. 978-3-527-30673-2 ↩

  4. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. ↩

  5. Igarashi, Masayasu; Matsumoto, Tomohiro; Yagihashi, Fujio; Yamashita, Hiroshi; Ohhara, Takashi; Hanashima, Takayasu; Nakao, Akiko; Moyoshi, Taketo; Sato, Kazuhiko; Shimada, Shigeru (2017). "Non-aqueous selective synthesis of orthosilicic acid and its oligomers". Nature Communications. 8 (1): 140. Bibcode:2017NatCo...8..140I. doi:10.1038/s41467-017-00168-5. PMC 5529440. PMID 28747652. S2CID 3832255. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5529440 ↩

  6. Igarashi, Masayasu; Matsumoto, Tomohiro; Yagihashi, Fujio; Yamashita, Hiroshi; Ohhara, Takashi; Hanashima, Takayasu; Nakao, Akiko; Moyoshi, Taketo; Sato, Kazuhiko; Shimada, Shigeru (2017). "Non-aqueous selective synthesis of orthosilicic acid and its oligomers". Nature Communications. 8 (1): 140. Bibcode:2017NatCo...8..140I. doi:10.1038/s41467-017-00168-5. PMC 5529440. PMID 28747652. S2CID 3832255. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5529440 ↩

  7. Farooq, Muhammad Ansar; Dietz, Karl-Josef (12 Nov 2015). "Silicon as Versatile Player in Plant and Human Biology: Overlooked and Poorly Understood". Frontiers in Plant Science. 6. Frontiers Media SA: 994. doi:10.3389/fpls.2015.00994. ISSN 1664-462X. PMC 4641902. PMID 26617630. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4641902 ↩

  8. Souri, Zahra; Khanna, Kanika; Karimi, Naser; Ahmad, Parvaiz (14 Jun 2020). "Silicon and Plants: Current Knowledge and Future Prospects". Journal of Plant Growth Regulation. 40 (3). Springer Science and Business Media LLC: 906–925. doi:10.1007/s00344-020-10172-7. ISSN 0721-7595. S2CID 253843062. /wiki/Doi_(identifier) ↩

  9. MA, Jian Feng; YAMAJI, Naoki; MITANI-UENO, Namiki (2011). "Transport of silicon from roots to panicles in plants". Proceedings of the Japan Academy, Series B. 87 (7). Japan Academy: 377–385. Bibcode:2011PJAB...87..377M. doi:10.2183/pjab.87.377. ISSN 0386-2208. PMC 3171283. PMID 21785256. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3171283 ↩

  10. Laane, Henk-Maarten (7 Jun 2018). "The Effects of Foliar Sprays with Different Silicon Compounds". Plants. 7 (2). MDPI AG: 45. doi:10.3390/plants7020045. ISSN 2223-7747. PMC 6027496. PMID 29880766. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027496 ↩

  11. Ratnakumar, P.; Deokate, P.P.; Rane, J.; Jain, N.; Kumar, V.; Berghe, D.V.; Minhas, P.S. (2016). "Effect of Ortho-Silicic Acid Exogenous Application on Wheat (Triticum aestivumL.) under Drought". Journal of Functional and Environmental Botany. 6 (1). Diva Enterprises Private Limited: 34. doi:10.5958/2231-1750.2016.00006.8. ISSN 2231-1742. /wiki/Doi_(identifier) ↩

  12. Goyal, Vinod; Baliyan, Vaibhav; Avtar, Ram; Mehrotra, Shweta (20 Aug 2022). "Alleviating Drought Stress in Brassica juncea (L.) Czern & Coss. by Foliar Application of Biostimulants—Orthosilicic Acid and Seaweed Extract". Applied Biochemistry and Biotechnology. 195 (1). Springer Science and Business Media LLC: 693–721. doi:10.1007/s12010-022-04085-2. ISSN 0273-2289. PMID 35986841. S2CID 251672735. /wiki/Doi_(identifier) ↩

  13. Dwivedi, Sanjay; Kumar, Amit; Mishra, Seema; Sharma, Pragya; Sinam, Geetgovind; Bahadur, Lal; Goyal, Vinod; Jain, Neeru; Tripathi, Rudra Deo (17 Apr 2020). "Orthosilicic acid (OSA) reduced grain arsenic accumulation and enhanced yield by modulating the level of trace element, antioxidants, and thiols in rice". Environmental Science and Pollution Research. 27 (19). Springer Science and Business Media LLC: 24025–24038. doi:10.1007/s11356-020-08663-x. ISSN 0944-1344. PMID 32301095. S2CID 215793851. /wiki/Doi_(identifier) ↩

  14. Imtiaz, Muhammad; Rizwan, Muhammad Shahid; Mushtaq, Muhammad Adnan; Ashraf, Muhammad; Shahzad, Sher Muhammad; Yousaf, Balal; Saeed, Dawood Anser; Rizwan, Muhammad; Nawaz, Muhammad Azher; Mehmood, Sajid; Tu, Shuxin (2016). "Silicon occurrence, uptake, transport and mechanisms of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review". Journal of Environmental Management. 183 (Pt 3). Elsevier BV: 521–529. doi:10.1016/j.jenvman.2016.09.009. ISSN 0301-4797. PMID 27623366. https://doi.org/10.1016%2Fj.jenvman.2016.09.009 ↩

  15. Coskun, Devrim; Britto, Dev T.; Huynh, Wayne Q.; Kronzucker, Herbert J. (18 Jul 2016). "The Role of Silicon in Higher Plants under Salinity and Drought Stress". Frontiers in Plant Science. 7. Frontiers Media SA: 1072. doi:10.3389/fpls.2016.01072. ISSN 1664-462X. PMC 4947951. PMID 27486474. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4947951 ↩

  16. Artyszak, Arkadiusz; Gozdowski, Dariusz (23 Jul 2021). "Influence of Various Forms of Foliar Application on Root Yield and Technological Quality of Sugar Beet". Agriculture. 11 (8). MDPI AG: 693. doi:10.3390/agriculture11080693. ISSN 2077-0472. https://doi.org/10.3390%2Fagriculture11080693 ↩

  17. Sharma, Divya; Sangwan, Sanyukta; Jain, Neeru (8 Sep 2020). "Antifungal Activity of Stabilized Ortho Silicic Acid (OSA) against Foliar Plant Pathogens". Silicon. 13 (11). Springer Science and Business Media LLC: 3807–3815. doi:10.1007/s12633-020-00628-6. ISSN 1876-990X. S2CID 221522347. /wiki/Doi_(identifier) ↩

  18. Fauteux, François; Rémus-Borel, Wilfried; Menzies, James G.; Bélanger, Richard R. (2005). "Silicon and plant disease resistance against pathogenic fungi". FEMS Microbiology Letters. 249 (1). Oxford University Press (OUP): 1–6. doi:10.1016/j.femsle.2005.06.034. ISSN 0378-1097. PMID 16006059. S2CID 17680350. https://doi.org/10.1016%2Fj.femsle.2005.06.034 ↩

  19. Coskun, Devrim; Deshmukh, Rupesh; Sonah, Humira; Menzies, James G.; Reynolds, Olivia; Ma, Jian Feng; Kronzucker, Herbert J.; Bélanger, Richard R. (14 Jul 2018). "The controversies of silicon's role in plant biology". New Phytologist. 221 (1). Wiley: 67–85. doi:10.1111/nph.15343. hdl:11343/284158. ISSN 0028-646X. PMID 30007071. S2CID 51628971. https://doi.org/10.1111%2Fnph.15343 ↩

  20. Bhaskar Mondal, Deepanwita Ghosh, and Abhijit K. Das (2009): "Thermochemistry for silicic acid formation reaction: Prediction of new reaction pathway". Chemical Physics Letters, volume 478, issues 4–6, pages 115-119. doi:10.1016/j.cplett.2009.07.063 /wiki/Doi_(identifier) ↩

  21. 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. ↩

  22. Treguer, P.; Nelson, D. M.; Van Bennekom, A. J.; DeMaster, D. J.; Leynaert, A.; Queguiner, B. (1995). "The silica balance in the world ocean: A reestimate". Science. 268 (5209): 375–379. Bibcode:1995Sci...268..375T. doi:10.1126/science.268.5209.375. PMID 17746543. S2CID 5672525. /wiki/Bibcode_(identifier) ↩

  23. Del Amo, Y., and M. A. Brzezinski. 1999. The chemical form of dissolved Si taken up by marine diatoms. J. Phycol. 35:1162-1170. https://onlinelibrary.wiley.com/doi/10.1046/j.1529-8817.1999.3561162.x/abstract https://onlinelibrary.wiley.com/doi/10.1046/j.1529-8817.1999.3561162.x/abstract ↩

  24. The figures here have been drawn using the interactive web site which feeds on annual DSi values from LEVITUS94: World Ocean Atlas 1994, an atlas of objectively analyzed fields of major ocean parameters at the annual, seasonal, and monthly time scales. Superseded by WOA98. Edited by Syd Levitus. /wiki/World_Ocean_Atlas ↩

  25. "World Ocean Atlas 1994". http://iridl.ldeo.columbia.edu/SOURCES/.LEVITUS94/ ↩