Industrial Inorganic Chemistry (CHEMY 348) 2022/2024 Chapter 3 Organosilicon Compounds PDF

Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Industrial Inorganic Chemistry (CHEMY 348) 2nd Semester 2022/2024 CHAPTER (3) Or...

Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Industrial Inorganic Chemistry (CHEMY 348) 2nd Semester 2022/2024 CHAPTER (3) Organosilicon Compounds Dr. Ahmed Abd El-Fattah Department of Chemistry, College of Science, University of Bahrain. Silicones Good Luck. Dr. Ahmed Abd El-Fattah 1 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 What are Organosilicon compounds? Organosilicon compounds are organometallic compounds containing carbon-silicon bonds.  Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Nomenclature SILICON Si O SILICA O Si O O X SILANES X Si X X X = halides ex. Cl R O Si O SILOXANES R R = alkyl or phenyl ex. CH3 ,C6H5 Good Luck. Dr. Ahmed Abd El-Fattah 2 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 What are Silicones or polyorganosiloxane?  Structure n up to 14000 Silicones are synthetic inorganic polymers with a linear, repeating silicon-oxygen (Si―O) polar backbone or chain and with organic groups (R) attached to the silicon atoms by C-Si bonds. The bond between silicon and oxygen molecule is very ionic in nature. Silicone polymers do not have carbon as part of the backbone structure. What are Silicones or polyorganosiloxane?  Structure n up to 14000 The Si-O bond energy is much larger than the C-C bond energy and this enables the -Si-O-framework of the silicone to give the polymers thermal stability. Depending on the number of repeat units (n) in the polymer chain and the degree of cross-linking, six classes of commercially important products can be produced. Good Luck. Dr. Ahmed Abd El-Fattah 3 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024  Properties  Silicones have unique properties amongst polymers because of the simultaneous presence of organic groups attached to a chain of inorganic atoms.  They are used in many industries including those devoted to electronics, paints, construction and food.  They are stable at high temperatures and are resistant to oxidation and weathering.  They are surface active hydrophobic (water-repellence) substances.  They are flexible polymers  They are adhesive, electrically non-conducting and exhibit high gas and vapor permeability.  Their physical properties also vary little with temperature. Structure and Properties  The most widely used silicones are those which have methyl groups along the backbone.  Properties such as solubility in organic solvents, water-repellence, high thermal stability and flexibility can be altered by substituting other organic groups for the methyl groups.  They are also better lubricants and are superior solvents for organic compounds.  The structure of the repeating units of silicones can be represented as: Where R represents organic groups attached to the silicone backbone, for example Good Luck. Dr. Ahmed Abd El-Fattah 4 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Manufacture of Silicones  Silicones are manufactured from pure silicon which has been obtained by the reduction of silicon dioxide (SiO2,silica) in the form of sand with carbon at high temperatures:  The production of silicones from silicon takes place in three stages: a) synthesis of chlorosilanes b) hydrolysis of chlorosilanes c) condensation polymerization or Polycondensation (a) Synthesis of chlorosilanes  Silicon is first converted into chlorosilanes, e.g. RSiCl3, R2SiCl2 and R3SiCl, where R is an organic group  When chloromethane is passed through heated silicon at about 550 K under slight pressure and in the presence of a copper catalyst (for example, brass or copper(II) chloride) a volatile mixture of chlorosilanes distils over. For example:  The mixture of liquids produced contains these three compounds Dimethyldichlorosilane  Careful distillation of the liquid mixture of chlorosilanes produces pure fractions of each chlorosilane. Dimethyldichlorosilane is the main product (70-90%, the amount depending on the conditions used). Good Luck. Dr. Ahmed Abd El-Fattah 5 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 (b) Hydrolysis of chlorosilanes A dichlorosilane is hydrolyzed to a molecule with two hydroxyl groups:  The product is a disilanol (siloxane diol). The suffix -ol in a silanol is to show that the molecule contains at least one hydroxyl group attached to a silicon atom and the simplest example is dimethyldisilanol  The hydroxyl groups of silanols react spontaneously to form linear siloxane oligomers (short chain polymers): Oligomers = short chains  If R is a methyl group, the polymer is a short chain poly(dimethylsiloxane).  Poly(dimethylsiloxanes) are produced with n = 20-50, which is not long enough to produce useful silicones.  These relatively short polymers are known as oligomers (n = 20-50). Good Luck. Dr. Ahmed Abd El-Fattah 6 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Cyclization  Reaction of siloxane oligomers with potassium hydroxide results in easy to separate and easily purified octamethylcyclotetrasiloxane. CH3 Si - O CH3 n n = 3 Trimer n = 4 Tetramer n = 5 Pentamer n = 6 Hexamer  The potassium hydroxide catalyzes the cyclization reaction of linear siloxane oligomers.  Octaimethylcyclotetrasiloxane is more volatile compared with linear siloxane. (c) Condensation polymerization or Polycondensation  The linear siloxane diols (disilanol) oligomers condense rapidly in the presence of an acid catalyst preferably phosphonitrile chlorides (PNCI2) to form long chain polymers (silicones):  The removal of the water liberated in the polycondensation process is achieved by operating the process at high temperatures and optionally under vacuum.  Deactivation of the catalyst is carried out with ammonia or amines. Good Luck. Dr. Ahmed Abd El-Fattah 7 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Uses of silicones The chemical structure of the silicones allow them to be produced in a variety of forms: a) Silicone fluids b) Silicone gels c) Silicone resins d) Silicone elastomers (rubbers) Their physical form and uses depend not only on the structure of the polymer, whether it is a short or long chain molecule, a three dimensional network or as a crosslinked species similar to a silicate, but also on the organic groups attached to the Si-O framework.  Silicone Classifications by Physical Form (1) Fluids (hydraulic, release agents, cosmetics, heat transfer media, polishes, lubricants, damping, dry cleaning) (2) Gels or Gums (high temperature heat transfer fluids, lubricants, greases, cosmetic and health care additives) (3) Resins (varnishes, protective coatings, release coatings, molding compounds, electronic insulation) (4) Elastomers (tubing and hoses, medical implants, sealants, adhesives, surgical aids, electrical insulation, fuel resistant rubber parts, rollers, etc) Good Luck. Dr. Ahmed Abd El-Fattah 8 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 (1) Silicone Fluids are typically straight chains of poly(dimethylsiloxane), with the repeating structure The silicones with short chains are fluids which, compared to hydrocarbons, have a more or less constant viscosity over a wide temperature range (200 to 450 K). They also have very low vapour pressures. The low surface tension of silicone fluids gives them unique surface properties. They are, for example, used as lubricants in polishes (a mixture of wax and a silicone fluid dissolved in an organic solvent), in paints and for water-proofing fabrics, paper and leather. They also have anti-foaming properties and have been used, for example, to suppress the foaming of detergents in sewage disposal plants and in domestic washing powders. This is because they have a very low surface tension and thus displace the surfactant molecules on the surface and depressing the ability of the surfactant to promote foam,. (2) Silicone Gels or Gums  They are based on poly(dimethylsiloxane) chains but with a few cross-links between the chains, giving it a very open three- dimensional network.  Often the cross-linking is done after a silicone fluid, together with a reactive group, is poured into a mold and then warmed or catalyzed so that there is interaction to form cross-linking between the polymer chains.  This is a very effective technique for protecting sensitive electronic equipment from damage from vibration and the polymer also acts as an electrical insulator. Pads containing a silicone gel are also used as shock absorbers in shoes, particularly in high-performance trainers and running shoes Good Luck. Dr. Ahmed Abd El-Fattah 9 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 (3) Silicone Resins  They have a three-dimensional structure with the atoms arranged tetrahedrally about the silicon atoms. The resins are usually applied as a solution in an organic solvent, and are used as an electrical insulating varnish or for paints where water repellence is desired, for example, to protect masonry. They are also used to give an 'anti- stick' surface to materials coming into contact with 'sticky' materials such as dough and other foodstuffs.  Hydroxyl groups on the resin react with hydroxyl groups that are on the surfaces of various inorganic surfaces such as silica and glass, thus making the surface water-repellent.  A large range of silanes, known as coupling agents, has been developed to enable chemists to bond an inorganic substrate (such as glass, minerals and metals) to organic materials (for example, organic polymers such as the acrylics, polyamides, urethanes and polyalkenes). Vulcanization is a chemical process by which rubber molecules are cross-linked with organic/inorganic substance (catalyst) or heat and pressure. The rubber which is cross linked chemically is known as vulcanizate. Good Luck. Dr. Ahmed Abd El-Fattah 10 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 (4) Silicone elastomers (rubbers)  They are made by introducing even more cross-linking into the linear chain polymers.  There are two main ways of doing this. 1. by adding a curing agent at Room Temperature–Vulcanizing (RTV), either using an organo-tin compound or with a platinum catalyst. 2. by adding a peroxide as a catalyst at an elevated temperature to produce what is termed as a High Temperature–Vulcanizing (HTV Silicone Rubber.  They are stable over a wide range of temperatures (200 to 450 K).  They are elastic, and their structure is somewhat similar to natural rubber and they behave as elastomers and the properties are determined by the amount of cross linking and the length of the chains. Hydroxyl groups on the resin react with hydroxyl groups that are on the surfaces of various inorganic surfaces such as silica and glass, thus making the surface water-repellent. SILICONES APPLICATIONS Dow Corning’s products and specialty materials are used by customers in virtually every major industry.  Aerospace  Medical Products  Automotive  Paints & Coatings  Chemicals/ Petrochemicals  Personal, Household & Automotive  Construction Care  Consumer Products  Pharmaceuticals  Electrical/Electronics  Plastics  Food Processing  Pressure-Sensitive Adhesives  Industrial Maintenance Production  Textiles & Leather Good Luck. Dr. Ahmed Abd El-Fattah 11 Industrial Inorganic Chemistry (CHEMY 348), Second 13 March 2024 Semester 2023/2024 Good Luck. Dr. Ahmed Abd El-Fattah 12