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The direct process, also called the direct synthesis, Rochow process, and Müller-Rochow process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and Richard Müller in the 1940s.^[1]^[2]

The process involves copper-catalyzed reactions of alkyl halides with elemental silicon, which take place in a fluidized bed reactor. Although theoretically possible with any alkyl halide, the best results in terms of selectivity and yield occur with chloromethane (CH₃Cl). Typical conditions are 300 °C and 2–5 bar. These conditions allow for 90–98% conversion for silicon and 30–90% for chloromethane. Approximately 1.4 Mton of dimethyldichlorosilane (Me₂SiCl₂) is produced annually using this process.^[3]

Few companies actually carry out the Rochow process, because of the complex technology and high capital requirements. Since the silicon is crushed prior to reaction in a fluidized bed, the companies practicing this technology are referred to as silicon crushers.^[4]

Reaction and mechanism

The relevant reactions are (Me = CH₃):

x MeCl + Si → Me₃SiCl, Me₂SiCl₂, MeSiCl₃, Me₄Si₂Cl₂, …

Dimethyldichlorosilane (Me₂SiCl₂) is of particular value (precursor to silicones), but trimethylsilyl chloride (Me₃SiCl) and methyltrichlorosilane (MeSiCl₃) are also valuable.^[5]^: 371

The mechanism of the direct process is still not well understood, despite much research. Copper plays an important role. The copper and silicon form intermetallics with the approximate composition Cu₃Si. This intermediate facilitates the formation of the Si-Cl and Si-Me bonds. It is proposed that close proximity of the Si-Cl to a copper-chloromethane "adduct" allows for formation of the Me-SiCl units. Transfer of a second chloromethane allows for the release of the Me₂SiCl₂. Thus, copper is oxidized from the zero oxidation state and then reduced to regenerate the catalyst.^[1]

The chain reaction can be terminated in many ways. These termination processes give rise to the other products that are seen in the reaction. For example, combining two Si-Cl groups gives the SiCl₂ group, which undergoes Cu-catalyzed reaction with MeCl to give MeSiCl₃.^[1]

In addition to copper, the catalyst optimally contains promoter metals that facilitate the reaction. Among the many promoter metals, zinc, tin, antimony, magnesium, calcium, bismuth, arsenic, and cadmium have been mentioned.^[1]^[3]

Product distribution and isolation

The major product for the direct process should be dichlorodimethylsilane, Me₂SiCl₂. However, many other products are formed. Unlike most reactions, this distribution is actually desirable because the product isolation is very efficient.^[1] Each methylchlorosilane has specific and often substantial applications. Me₂SiCl₂ is the most useful. It is the precursor for the majority of silicon products produced on an industrial scale. The other products are used in the preparation of siloxane polymers as well as specialized applications.^[1]

Dichlorodimethylsilane is the major product of the reaction, as is expected, being obtained in about 70–90% yield. The next most abundant product is methyltrichlorosilane (MeSiCl₃), at 5–15% of the total. Other products include Me₃SiCl (2–4%), MeHSiCl₂ (1–4%), and Me₂HSiCl (0.1–0.5%).^[1]

The Me₂SiCl₂ is purified by fractional distillation. Although the boiling points of the various chloromethylsilanes are similar (Me₂SiCl₂: 70 °C, MeSiCl₃: 66 °C, Me₃SiCl: 57 °C, MeHSiCl₂: 41 °C, Me₂HSiCl: 35 °C), the distillation utilizes columns with high separating capacities, connected in series. The purity of the products crucially affects the production of siloxane polymers, otherwise chain branching arises.^[1]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h Rösch, L.; John, P.; Reitmeier, R. (2003). "Organic Silicon Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_021. ISBN 978-3527306732..
^ Pachaly, B.; Weis, J. (1997). "The Direct Process to Methylchlorosilanes: Reflections on Chemistry and Process Technology". Organosilicon Chemistry III. pp. 478–483. doi:10.1002/9783527619900.ch79. ISBN 978-3-527-29450-3.
^ ^a ^b Elschenbroich, Christoph Organometallics VCH, Weinheim, Germany: 1992. ISBN 978-3-527-29390-2.
^ "Basic Silicone Chemistry – A Review" (PDF). Archived from the original (PDF) on 2011-05-16. Retrieved 2010-01-26.
^ Shriver & Atkins' inorganic chemistry. P. W. Atkins (5 ed.). Oxford: Oxford University Press. 2010. ISBN 978-0-19-923617-6. OCLC 430678988.{{cite book}}: CS1 maint: others (link)

[Roesch-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h Rösch, L.; John, P.; Reitmeier, R. (2003). "Organic Silicon Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_021. ISBN 978-3527306732..

[2] Pachaly, B.; Weis, J. (1997). "The Direct Process to Methylchlorosilanes: Reflections on Chemistry and Process Technology". Organosilicon Chemistry III. pp. 478–483. doi:10.1002/9783527619900.ch79. ISBN 978-3-527-29450-3.

[Elschenbroich-3] Elschenbroich, Christoph Organometallics VCH, Weinheim, Germany: 1992. ISBN 978-3-527-29390-2.

[4] "Basic Silicone Chemistry – A Review" (PDF). Archived from the original (PDF) on 2011-05-16. Retrieved 2010-01-26.

[5] Shriver & Atkins' inorganic chemistry. P. W. Atkins (5 ed.). Oxford: Oxford University Press. 2010. ISBN 978-0-19-923617-6. OCLC 430678988.{{cite book}}: CS1 maint: others (link)

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-The '''Direct Process''', also called the '''Direct synthesis''', is the most common technology for preparing [[organosilicon]] compounds on an industrial scale. It was first reported independently by [[Eugene G. Rochow]] and [[Richard Müller (chemist)|Richard Müller]]  in the 1940s.<ref name=Roeshe>Röshe, L.; John, P.; Reitmeier, R.  “Organic Silicon Compounds”  Ullmann’s Encyclopedia of Industrial Chemistry.  John Wiley and Sons: San Francisco, 2003.  {{DOI|10.1002/14356007.a24_021}}.</ref>  The reaction involves a copper-catalyzed reaction of alkyl halides with silicon metal, which takes place in a fluidized bed reactor.  Although theoretically possible with any type of alkyl halide, the best results in terms of selectivity and yield occur with chloromethane.  Typical conditions are 300 °C and 2-5 bar.  These conditions allow for 90-98% conversion for silicon and 30-90% for chloromethane.  Approximately 1.4 Mton of Me<sub>2</sub>SiCl<sub>2</sub> is produced annually using this process.<ref name=Elschenbroich>Elschenbroich, Christoph Organometallics VCH, Weinheim, Germany: 1992.  ISBN: 978-3527293902.</ref>
+The '''direct process''', also called the '''direct synthesis''', '''Rochow process''', and '''Müller-Rochow process''' is the most common technology for preparing [[organosilicon]] compounds on an industrial scale. It was first reported independently by [[Eugene G. Rochow]] and [[Richard Müller (chemist)|Richard Müller]] in the 1940s.<ref name=Roesch>{{Ullmann|author=Rösch, L.|author2=John, P.|author3=Reitmeier, R.|title=Organic Silicon Compounds|year=2003|doi=10.1002/14356007.a24_021}}.</ref><ref>{{cite book |doi=10.1002/9783527619900.ch79 |chapter=The Direct Process to Methylchlorosilanes: Reflections on Chemistry and Process Technology |title=Organosilicon Chemistry III |date=1997 |last1=Pachaly |first1=B. |last2=Weis |first2=J. |pages=478–483 |isbn=978-3-527-29450-3 }}</ref>
+The process involves copper-catalyzed reactions of alkyl halides with elemental silicon, which take place in a [[fluidized bed reactor]]. Although theoretically possible with any alkyl halide, the best results in terms of selectivity and yield occur with [[chloromethane]] (CH<sub>3</sub>Cl). Typical conditions are 300{{nbsp}}°C and 2–5{{nbsp}}bar. These conditions allow for 90–98% conversion for silicon and 30–90% for chloromethane. Approximately 1.4 Mton of [[dimethyldichlorosilane]] (Me<sub>2</sub>SiCl<sub>2</sub>) is produced annually using this process.<ref name=Elschenbroich>Elschenbroich, Christoph Organometallics VCH, Weinheim, Germany: 1992. {{ISBN|978-3-527-29390-2}}.</ref>
+Few companies actually carry out the Rochow process, because of the complex technology and high capital requirements. Since the [[silicon]] is [[wiktionary:crushed|crushed]] prior to reaction in a [[fluidized bed]], the companies practicing this technology are referred to as ''silicon crushers''.<ref>{{Cite web |url=http://www.siliconespectator.com/articles/Silicone_Spectator_January_2009.pdf |title=Basic Silicone Chemistry – A Review |access-date=2010-01-26 |archive-url=https://web.archive.org/web/20110516234405/http://www.siliconespectator.com/articles/Silicone_Spectator_January_2009.pdf |archive-date=2011-05-16 |url-status=dead}}</ref>
 ==Reaction and mechanism==
 The relevant reactions are (Me = CH<sub>3</sub>):
-:MeCl + Si → Me<sub>3</sub>SiCl, Me<sub>2</sub>SiCl<sub>2</sub>, MeSiCl<sub>3</sub>, other products
+: x MeCl + Si → Me<sub>3</sub>SiCl, Me<sub>2</sub>SiCl<sub>2</sub>, MeSiCl<sub>3</sub>, Me<sub>4</sub>Si<sub>2</sub>Cl<sub>2</sub>, …
+[[Dimethyldichlorosilane]] (Me<sub>2</sub>SiCl<sub>2</sub>) is of particular value (precursor to [[silicone]]s), but [[trimethylsilyl chloride]] (Me<sub>3</sub>SiCl) and [[methyltrichlorosilane]] (MeSiCl<sub>3</sub>) are also valuable.<ref>{{Cite book |url=https://www.worldcat.org/oclc/430678988 |title=Shriver & Atkins' inorganic chemistry |date=2010 |publisher=Oxford University Press |others=P. W. Atkins |isbn=978-0-19-923617-6 |edition=5 |location=Oxford |oclc=430678988}}</ref>{{Rp|page=371}}
-The mechanism of the direct process is still not well understood, despite much research.  [[Copper]] plays an important role.  The copper and silicon form an intermetallic with the approximate composition Cu<sub>3</sub>Si.  This intermediate facilitates the formation of the Si-Cl and Si-Me bonds.  It is proposed that close proximity of the Si-Cl to a copper-chloromethane “adduct” allows for formation of the Me-SiCl units.  Transfer of a second chloromethane allows for the release of the Me<sub>2</sub>SiCl<sub>2</sub>.  Thus, copper is oxidized from the zero oxidation state and then reduced to regenerate the catalyst.<ref name=Roeshe/>
+The mechanism of the direct process is still not well understood, despite much research. [[Copper]] plays an important role. The copper and silicon form [[intermetallic]]s with the approximate composition Cu<sub>3</sub>Si. This intermediate facilitates the formation of the Si-Cl and Si-Me bonds. It is proposed that close proximity of the Si-Cl to a copper-chloromethane "adduct" allows for formation of the Me-SiCl units. Transfer of a second chloromethane allows for the release of the Me<sub>2</sub>SiCl<sub>2</sub>. Thus, copper is oxidized from the zero oxidation state and then reduced to regenerate the catalyst.<ref name=Roesch/>
-The chain reaction can be terminated in many ways.  These termination processes give rise to the other products that are seen in the reaction.  For example, combining two Si-Cl groups gives the SiCl<sub>2</sub> group, which undergoes Cu-catalyzed reaction with MeCl to give MeSiCl<sub>3</sub>.<ref name=Roeshe/>
+The chain reaction can be terminated in many ways. These termination processes give rise to the other products that are seen in the reaction. For example, combining two Si-Cl groups gives the SiCl<sub>2</sub> group, which undergoes Cu-catalyzed reaction with MeCl to give MeSiCl<sub>3</sub>.<ref name=Roesch/>
-In addition to copper, the catalyst optimally contains promoter metals that facilitate the reaction.  Among the many promoter metals, zinc, tin, antimony, magnesium, calcium, bismuth, arsenic and cadmium have been mentioned.<ref name=Roeshe/>
-,<ref name=Elschenbroich/>
+In addition to copper, the catalyst optimally contains promoter metals that facilitate the reaction. Among the many promoter metals, zinc, tin, antimony, magnesium, calcium, bismuth, arsenic, and cadmium have been mentioned.<ref name=Roesch/><ref name=Elschenbroich/>
 ==Product distribution and isolation==
-The major product for the direct process should be dichlorodimethylsilane, Me<sub>2</sub>SiCl<sub>2</sub>.  However, many other products are formed.  Unlike most reactions, this distribution is actually desirable because the product isolation is very efficient.<ref name=Roeshe/>  Each methylchlorosilane has specific and often substantial applications.  Me<sub>2</sub>SiCl<sub>2</sub> is the most useful.  It is the precursor for the majority of silicon products produced on an industrial scale.  The other products are used in the preparation of siloxane polymers as well as specialized applications.<ref name=Roeshe/>
+The major product for the direct process should be dichlorodimethylsilane, Me<sub>2</sub>SiCl<sub>2</sub>. However, many other products are formed. Unlike most reactions, this distribution is actually desirable because the product isolation is very efficient.<ref name=Roesch/> Each methylchlorosilane has specific and often substantial applications. Me<sub>2</sub>SiCl<sub>2</sub> is the most useful. It is the precursor for the majority of silicon products produced on an industrial scale. The other products are used in the preparation of siloxane polymers as well as specialized applications.<ref name=Roesch/>
-Dichlorodimethylsilane is the major product of the reaction, as is expected, being obtained in about 70-90% yield.  The next most abundant product is MeSiCl<sub>3</sub>, at 5-15% of the total.  Other products include Me<sub>3</sub>SiCl (2-4%), MeHSiCl<sub>2</sub>  (1-4%), and Me<sub>2</sub>HSiCl (0.1-0.5%).<ref name=Roeshe/>
+Dichlorodimethylsilane is the major product of the reaction, as is expected, being obtained in about 70–90% yield. The next most abundant product is [[methyltrichlorosilane]] (MeSiCl<sub>3</sub>), at 5–15% of the total. Other products include Me<sub>3</sub>SiCl (2–4%), MeHSiCl<sub>2</sub> (1–4%), and Me<sub>2</sub>HSiCl (0.1–0.5%).<ref name=Roesch/>
-The Me<sub>2</sub>SiCl<sub>2</sub> is purified by [[fractional distillation]].  Although the boiling points of the various chloro methyl silanes are similar (Me<sub>2</sub>SiCl<sub>2</sub>:70 C, MeSiCl<sub>3</sub>: 66 C, Me<sub>3</sub>SiCl: 57 C, MeHSiCl<sub>2</sub>: 41 C, Me<sub>2</sub>HSiCl: 35 C), the distillation utilizes columns with high separating capacities, connected in series.  The purity of the products crucially affects the production of siloxane polymers, otherwise chain branching arises.<ref name=Roeshe/>
+The Me<sub>2</sub>SiCl<sub>2</sub> is purified by [[fractional distillation]]. Although the boiling points of the various chloromethylsilanes are similar (Me<sub>2</sub>SiCl<sub>2</sub>: 70{{nbsp}}°C, MeSiCl<sub>3</sub>: 66{{nbsp}}°C, Me<sub>3</sub>SiCl: 57{{nbsp}}°C, MeHSiCl<sub>2</sub>: 41{{nbsp}}°C, Me<sub>2</sub>HSiCl: 35{{nbsp}}°C), the distillation utilizes columns with high separating capacities, connected in series. The purity of the products crucially affects the production of siloxane polymers, otherwise chain branching arises.<ref name=Roesch/>
 ==References==
+{{Reflist}}
-<references/>
+{{Chemical synthesis}}
+{{Authority control}}
 [[Category:Chemical synthesis]]
-[[Category:Chemical reactions]]
+[[Category:Silicon]]