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69-515: Ziegler–Natta catalysts are used to polymerize terminal alkenes (ethylene and alkenes with the vinyl double bond): The 1963 Nobel Prize in Chemistry was awarded to German Karl Ziegler , for his discovery of first titanium-based catalysts, and Italian Giulio Natta , for using them to prepare stereoregular polymers from propylene . Ziegler–Natta catalysts have been used in the commercial manufacture of various polyolefins since 1956. As of 2010,

138-521: A carbocation . The net result of the reaction will be an alcohol . The reaction equation for hydration of ethylene is: Hydrohalogenation involves addition of H−X to unsaturated hydrocarbons. This reaction results in new C−H and C−X σ bonds. The formation of the intermediate carbocation is selective and follows Markovnikov's rule . The hydrohalogenation of alkene will result in haloalkane . The reaction equation of HBr addition to ethylene is: Alkenes add to dienes to give cyclohexenes . This conversion

207-474: A δ H of 4.5–6.5  ppm . The double bond will also deshield the hydrogen attached to the carbons adjacent to sp carbons, and this generates δ H =1.6–2. ppm peaks. Cis/trans isomers are distinguishable due to different J-coupling effect. Cis vicinal hydrogens will have coupling constants in the range of 6–14  Hz , whereas the trans will have coupling constants of 11–18 Hz. In their C NMR spectra of alkenes, double bonds also deshield

276-523: A C=C π bond in unsaturated hydrocarbons weakens the dissociation energy of the allylic C−H bonds. Thus, these groupings are susceptible to free radical substitution at these C-H sites as well as addition reactions at the C=C site. In the presence of radical initiators , allylic C-H bonds can be halogenated. The presence of two C=C bonds flanking one methylene, i.e., doubly allylic, results in particularly weak HC-H bonds. The high reactivity of these situations

345-405: A carbon chain, or at least one functional group attached to each carbon is the same for both. E- and Z- configuration can be used instead in a more general case where all four functional groups attached to carbon atoms in a double bond are different. E- and Z- are abbreviations of German words zusammen (together) and entgegen (opposite). In E- and Z-isomerism, each functional group is assigned

414-460: A double bond cannot occur at the bridgehead of a bridged ring system unless the rings are large enough. Following Fawcett and defining S as the total number of non-bridgehead atoms in the rings, bicyclic systems require S  ≥ 7 for stability and tricyclic systems require S  ≥ 11. In organic chemistry ,the prefixes cis- and trans- are used to describe the positions of functional groups attached to carbon atoms joined by

483-434: A double bond. In Latin, cis and trans mean "on this side of" and "on the other side of" respectively. Therefore, if the functional groups are both on the same side of the carbon chain, the bond is said to have cis- configuration, otherwise (i.e. the functional groups are on the opposite side of the carbon chain), the bond is said to have trans- configuration. For there to be cis- and trans- configurations, there must be

552-840: A feedstock for the petrochemical industry because they can participate in a wide variety of reactions, prominently polymerization and alkylation. Except for ethylene, alkenes have two sites of reactivity: the carbon–carbon pi-bond and the presence of allylic CH centers. The former dominates but the allylic sites are important too. Hydrogenation involves the addition of H 2 resulting in an alkane. The equation of hydrogenation of ethylene to form ethane is: Hydrogenation reactions usually require catalysts to increase their reaction rate . The total number of hydrogens that can be added to an unsaturated hydrocarbon depends on its degree of unsaturation . Similar to hydrogen, halogens added to double bonds. Halonium ions are intermediates. These reactions do not require catalysts. Bromine test

621-591: A more reliable β-elimination method than E1 for most alkene syntheses. Most E2 eliminations start with an alkyl halide or alkyl sulfonate ester (such as a tosylate or triflate ). When an alkyl halide is used, the reaction is called a dehydrohalogenation . For unsymmetrical products, the more substituted alkenes (those with fewer hydrogens attached to the C=C) tend to predominate (see Zaitsev's rule ). Two common methods of elimination reactions are dehydrohalogenation of alkyl halides and dehydration of alcohols. A typical example

690-488: A priority based on the Cahn–Ingold–Prelog priority rules . If the two groups with higher priority are on the same side of the double bond, the bond is assigned Z- configuration, otherwise (i.e. the two groups with higher priority are on the opposite side of the double bond), the bond is assigned E- configuration. Cis- and trans- configurations do not have a fixed relationship with E - and Z -configurations. Many of

759-402: A process that forms hydrogen chloride : In some cases, TiCl 4 is oxidised directly with oxygen : It has been used to produce smoke screens since it produces a heavy, white smoke that has little tendency to rise. "Tickle" was the standard means of producing on-set smoke effects for motion pictures, before being phased out in the 1980s due to concerns about hydrated HCl 's effects on

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828-495: A reaction of ethylene with the organometallic compound triethylaluminium in the presence of nickel , cobalt , or platinum . One of the principal methods for alkene synthesis in the laboratory is the elimination reaction of alkyl halides, alcohols, and similar compounds. Most common is the β-elimination via the E2 or E1 mechanism. A commercially significant example is the production of vinyl chloride . The E2 mechanism provides

897-467: A typical C-C single bond. Each carbon atom of the double bond uses its three sp hybrid orbitals to form sigma bonds to three atoms (the other carbon atom and two hydrogen atoms). The unhybridized 2p atomic orbitals, which lie perpendicular to the plane created by the axes of the three sp hybrid orbitals, combine to form the pi bond. This bond lies outside the main C–C axis, with half of the bond on one side of

966-496: A yellow, benzene-soluble liquid: This molecule is tetrahedral, with planar nitrogen centers. TiCl 4 is a Lewis acid as implicated by its tendency to hydrolyze . With the ether THF , TiCl 4 reacts to give yellow crystals of TiCl 4 (THF) 2 . With chloride salts, TiCl 4 reacts to form sequentially [Ti 2 Cl 9 ] , [Ti 2 Cl 10 ] (see figure above), and [TiCl 6 ] . The reaction of chloride ions with TiCl 4 depends on

1035-578: A β-hydride elimination reaction also occurs periodically: Polymerization reactions of alkenes with solid titanium-based catalysts occur at special titanium centers located on the exterior of the catalyst crystallites. Some titanium atoms in these crystallites react with organoaluminum cocatalysts with the formation of Ti–C bonds. The polymerization reaction of alkenes occurs similarly to the reactions in metallocene catalysts: The two chain termination reactions occur quite rarely in Ziegler–Natta catalysis and

1104-426: Is microporous spheres of amorphous silica with a diameter of 30–40 mm. During the catalyst synthesis, both the titanium compounds and MgCl 2 are packed into the silica pores. All these catalysts are activated with organoaluminum compounds such as Al(C 2 H 5 ) 3 . All modern supported Ziegler–Natta catalysts designed for polymerization of propylene and higher 1-alkenes are prepared with TiCl 4 as

1173-468: Is titanium isopropoxide , which is a monomer. Titanium bis(acetylacetonate)dichloride results from treatment of titanium tetrachloride with excess acetylacetone : Organic amines react with TiCl 4 to give complexes containing amido ( R 2 N -containing) and imido ( RN -containing) complexes. With ammonia, titanium nitride is formed. An illustrative reaction is the synthesis of tetrakis(dimethylamido)titanium Ti(N(CH 3 ) 2 ) 4 ,

1242-478: Is an aluminium-containing derivative of titanocene that arises from the reaction of titanocene dichloride with trimethylaluminium . It is used for the "olefination" reactions. Arenes , such as C 6 (CH 3 ) 6 react to give the piano-stool complexes [Ti(C 6 R 6 )Cl 3 ] (R = H, CH 3 ; see figure above). This reaction illustrates the high Lewis acidity of the TiCl + 3 entity, which

1311-561: Is an example of a Diels-Alder reaction . Such reaction proceed with retention of stereochemistry. The rates are sensitive to electron-withdrawing or electron-donating substituents. When irradiated by UV-light, alkenes dimerize to give cyclobutanes . Another example is the Schenck ene reaction , in which singlet oxygen reacts with an allylic structure to give a transposed allyl peroxide : Alkenes react with percarboxylic acids and even hydrogen peroxide to yield epoxides : For ethylene,

1380-406: Is an important intermediate in the production of titanium metal and the pigment titanium dioxide . TiCl 4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide ( TiO 2 ) and hydrochloric acid , a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of

1449-424: Is catalytic dehydrogenation , where an alkane loses hydrogen at high temperatures to produce a corresponding alkene. This is the reverse of the catalytic hydrogenation of alkenes. This process is also known as reforming . Both processes are endothermic and are driven towards the alkene at high temperatures by entropy . Catalytic synthesis of higher α-alkenes (of the type RCH=CH 2 ) can also be achieved by

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1518-425: Is formed scatter light very efficiently. This smoke is corrosive, however. Alcohols react with TiCl 4 to give alkoxides with the formula [Ti(OR) 4 ] n (R = alkyl , n = 1, 2, 4). As indicated by their formula, these alkoxides can adopt complex structures ranging from monomers to tetramers. Such compounds are useful in materials science as well as organic synthesis . A well known derivative

1587-657: Is generated by abstraction of chloride from TiCl 4 by AlCl 3 . TiCl 4 finds occasional use in organic synthesis , capitalizing on its Lewis acidity , its oxophilicity , and the electron-transfer properties of its reduced titanium halides. It is used in the Lewis acid catalysed aldol addition Key to this application is the tendency of TiCl 4 to activate aldehydes (RCHO) by formation of adducts such as (RCHO)TiCl 4 OC(H)R . Hazards posed by titanium tetrachloride generally arise from its reaction with water that releases hydrochloric acid , which

1656-551: Is illustrated in the picture on the left with polypropylene. Stereoregular poly(1-alkene) can be isotactic or syndiotactic depending on the relative orientation of the alkyl groups in polymer chains consisting of units −[CH 2 −CHR]−, like the CH 3 groups in the figure. In the isotactic polymers, all stereogenic centers CHR share the same configuration. The stereogenic centers in syndiotactic polymers alternate their relative configuration. A polymer that lacks any regular arrangement in

1725-456: Is itself called allene —and those with three or more overlapping bonds ( C=C=C=C , C=C=C=C=C , etc.) are called cumulenes . Alkenes having four or more carbon atoms can form diverse structural isomers . Most alkenes are also isomers of cycloalkanes . Acyclic alkene structural isomers with only one double bond follow: Many of these molecules exhibit cis – trans isomerism . There may also be chiral carbon atoms particularly within

1794-515: Is made from TiCl 4 . The conversion involves the reduction of the tetrachloride with magnesium metal. This procedure is known as the Kroll process : In the Hunter process , liquid sodium is the reducing agent instead of magnesium. Around 90% of the TiCl 4 production is used to make the pigment titanium dioxide ( TiO 2 ). The conversion involves hydrolysis of TiCl 4 ,

1863-438: Is relatively small because the requirements to the respective catalysts differ widely. Commercial catalysts are supported by being bound to a solid with a high surface area. Both TiCl 4 and TiCl 3 give active catalysts. The support in the majority of the catalysts is MgCl 2 . A third component of most catalysts is a carrier, a material that determines the size and the shape of catalyst particles. The preferred carrier

1932-476: Is shown below; note that if possible, the H is anti to the leaving group, even though this leads to the less stable Z -isomer. Alkenes can be synthesized from alcohols via dehydration , in which case water is lost via the E1 mechanism. For example, the dehydration of ethanol produces ethylene: Titanium tetrachloride Titanium tetrachloride is the inorganic compound with the formula TiCl 4 . It

2001-587: Is soluble in toluene and chlorocarbons . Certain arenes form complexes of the type [(C 6 R 6 )TiCl 3 ] . TiCl 4 reacts exothermically with donor solvents such as THF to give hexacoordinated adducts . Bulkier ligands (L) give pentacoordinated adducts TiCl 4 L . TiCl 4 is produced by the chloride process , which involves the reduction of titanium oxide ores, typically ilmenite ( FeTiO 3 ), with carbon under flowing chlorine at 900 °C. Impurities are removed by distillation . The coproduction of FeCl 3

2070-637: Is the [4+2]- cycloaddition of singlet oxygen with a diene such as cyclopentadiene to yield an endoperoxide : Terminal alkenes are precursors to polymers via processes termed polymerization . Some polymerizations are of great economic significance, as they generate the plastics polyethylene and polypropylene . Polymers from alkene are usually referred to as polyolefins although they contain no olefins. Polymerization can proceed via diverse mechanisms. Conjugated dienes such as buta-1,3-diene and isoprene (2-methylbuta-1,3-diene) also produce polymers, one example being natural rubber. The presence of

2139-402: Is the basis for certain free radical reactions, manifested in the chemistry of drying oils . Alkenes undergo olefin metathesis , which cleaves and interchanges the substituents of the alkene. A related reaction is ethenolysis : In transition metal alkene complexes , alkenes serve as ligands for metals. In this case, the π electron density is donated to the metal d orbitals. The stronger

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2208-474: Is transformed into a metallocenium ion Cp 2 + Zr CH 3 , which is ion-paired to some derivative(s) of MAO. A polymer molecule grows by numerous insertion reactions of C=C bonds of 1-alkene molecules into the Zr–C bond in the ion: Many thousands of alkene insertion reactions occur at each active center resulting in the formation of long polymer chains attached to the center. The Cossee–Arlman mechanism describes

2277-586: Is undesirable, which has motivated the development of alternative technologies. Instead of directly using ilmenite, "rutile slag" is used. This material, an impure form of TiO 2 , is derived from ilmenite by removal of iron, either using carbon reduction or extraction with sulfuric acid . Crude TiCl 4 contains a variety of other volatile halides, including vanadyl chloride ( VOCl 3 ), silicon tetrachloride ( SiCl 4 ), and tin tetrachloride ( SnCl 4 ), which must be separated. The world's supply of titanium metal, about 250,000 tons per year,

2346-595: Is used to test the saturation of hydrocarbons. The bromine test can also be used as an indication of the degree of unsaturation for unsaturated hydrocarbons. Bromine number is defined as gram of bromine able to react with 100g of product. Similar as hydrogenation, the halogenation of bromine is also depend on the number of π bond. A higher bromine number indicates higher degree of unsaturation. The π bonds of alkenes hydrocarbons are also susceptible to hydration . The reaction usually involves strong acid as catalyst . The first step in hydration often involves formation of

2415-412: The E – Z notation for molecules with three or four different substituents (side groups). For example, of the isomers of butene , the two methyl groups of ( Z )-but-2 -ene (a.k.a. cis -2-butene) appear on the same side of the double bond, and in ( E )-but-2-ene (a.k.a. trans -2-butene) the methyl groups appear on opposite sides. These two isomers of butene have distinct properties. As predicted by

2484-532: The VSEPR model of electron pair repulsion, the molecular geometry of alkenes includes bond angles about each carbon atom in a double bond of about 120°. The angle may vary because of steric strain introduced by nonbonded interactions between functional groups attached to the carbon atoms of the double bond. For example, the C–C–C bond angle in propylene is 123.9°. For bridged alkenes, Bredt's rule states that

2553-493: The epoxidation is conducted on a very large scale industrially using oxygen in the presence of silver-based catalysts: Alkenes react with ozone, leading to the scission of the double bond. The process is called ozonolysis . Often the reaction procedure includes a mild reductant, such as dimethylsulfide ( SMe 2 ): When treated with a hot concentrated, acidified solution of KMnO 4 , alkenes are cleaved to form ketones and/or carboxylic acids . The stoichiometry of

2622-452: The 1960s, BASF developed a gas-phase, mechanically-stirred polymerization process for making polypropylene . In that process, the particle bed in the reactor was either not fluidized or not fully fluidized. In 1968, the first gas-phase fluidized-bed polymerization process, the Unipol process, was commercialized by Union Carbide to produce polyethylene. In the mid-1980s, the Unipol process

2691-526: The US and Mideast and naphtha in Europe and Asia. Alkanes are broken apart at high temperatures, often in the presence of a zeolite catalyst, to produce a mixture of primarily aliphatic alkenes and lower molecular weight alkanes. The mixture is feedstock and temperature dependent, and separated by fractional distillation. This is mainly used for the manufacture of small alkenes (up to six carbons). Related to this

2760-451: The active ingredient and MgCl 2 as a support. Another component of all such catalysts is an organic modifier, usually an ester of an aromatic diacid or a diether . The modifiers react both with inorganic ingredients of the solid catalysts as well as with organoaluminum cocatalysts. These catalysts polymerize propylene and other 1-alkenes to highly crystalline isotactic polymers. A second class of Ziegler–Natta catalysts are soluble in

2829-411: The alkylaluminium compounds are pyrophoric . The catalysts, therefore, are always prepared and handled under an inert atmosphere. The structure of active centers in Ziegler–Natta catalysts is well established only for metallocene catalysts. An idealized and simplified metallocene complex Cp 2 ZrCl 2 represents a typical precatalyst. It is unreactive toward alkenes. The dihalide reacts with MAO and

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2898-466: The boiling and melting points of various alkenes with the corresponding alkane and alkyne analogues. In the IR spectrum, the stretching/compression of C=C bond gives a peak at 1670–1600  cm . The band is weak in symmetrical alkenes. The bending of C=C bond absorbs between 1000 and 650 cm wavelength In H NMR spectroscopy, the hydrogen bonded to the carbon adjacent to double bonds will give

2967-616: The carbons, making them have low field shift. C=C double bonds usually have chemical shift of about 100–170 ppm. Like most other hydrocarbons , alkenes combust to give carbon dioxide and water. The combustion of alkenes release less energy than burning same molarity of saturated ones with same number of carbons. This trend can be clearly seen in the list of standard enthalpy of combustion of hydrocarbons. Alkenes are relatively stable compounds, but are more reactive than alkanes . Most reactions of alkenes involve additions to this pi bond, forming new single bonds . Alkenes serve as

3036-425: The chloride atoms bridge between the metals. Its melting point is similar to that of CCl 4 . Ti has a "closed" electronic shell, with the same number of electrons as the noble gas argon . The tetrahedral structure for TiCl 4 is consistent with its description as a d metal center ( Ti ) surrounded by four identical ligands. This configuration leads to highly symmetrical structures, hence

3105-573: The counterion. [N(CH 2 CH 2 CH 2 CH 3 ) 4 ]Cl and TiCl 4 gives the pentacoordinate complex [N(CH 2 CH 2 CH 2 CH 3 ) 4 ][TiCl 5 ] , whereas smaller [N(CH 2 CH 3 ) 4 ] gives [N(CH 2 CH 3 ) 4 ] 2 [Ti 2 Cl 10 ] . These reactions highlight the influence of electrostatics on the structures of compounds with highly ionic bonding. Reduction of TiCl 4 with aluminium results in one-electron reduction. The trichloride ( TiCl 3 ) and tetrachloride have contrasting properties:

3174-493: The development of fully amorphous copolymers. The fluidized-bed process remains one of the two most widely used processes for producing polypropylene . Natta first used polymerization catalysts based on titanium chlorides to polymerize propylene and other 1-alkenes. He discovered that these polymers are crystalline materials and ascribed their crystallinity to a special feature of the polymer structure called stereoregularity . The concept of stereoregularity in polymer chains

3243-559: The donation is, the stronger the back bonding from the metal d orbital to π* anti-bonding orbital of the alkene. This effect lowers the bond order of the alkene and increases the C-C bond length . One example is the complex PtCl 3 (C 2 H 4 )] . These complexes are related to the mechanisms of metal-catalyzed reactions of unsaturated hydrocarbons. Alkenes are produced by hydrocarbon cracking . Raw materials are mostly natural-gas condensate components (principally ethane and propane) in

3312-462: The formed polymers have a too high molecular weight to be of commercial use. To reduce the molecular weight, hydrogen is added to the polymerization reaction: Another termination process involves the action of protic (acidic) reagents, which can be intentionally added or adventitious. Alkene In organic chemistry , an alkene , or olefin , is a hydrocarbon containing a carbon –carbon double bond . The double bond may be internal or in

3381-439: The general class – cyclic or acyclic, with one or more double bonds. Acyclic alkenes, with only one double bond and no other functional groups (also known as mono-enes ) form a homologous series of hydrocarbons with the general formula C n H 2 n with n being a >1 natural number (which is two hydrogens less than the corresponding alkane ). When n is four or more, isomers are possible, distinguished by

3450-484: The growth of stereospecific polymers. This mechanism states that the polymer grows through alkene coordination at a vacant site at the titanium atom, which is followed by insertion of the C=C bond into the Ti−C bond at the active center. On occasion, the polymer chain is disengaged from the active centers in the chain termination reaction. Several pathways exist for termination: Another type of chain termination reaction called

3519-447: The larger molecules (from C 5 ). The number of potential isomers increases rapidly with additional carbon atoms. A carbon–carbon double bond consists of a sigma bond and a pi bond . This double bond is stronger than a single covalent bond (611  kJ / mol for C=C vs. 347 kJ/mol for C–C), but not twice as strong. Double bonds are shorter than single bonds with an average bond length of 1.33 Å (133 pm ) vs 1.53 Å for

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3588-711: The low-temperature polymerization of ethylene, which launched major industrial technologies culminating in the Phillips catalyst . A few years later, Ziegler discovered that a combination of titanium tetrachloride (TiCl 4 ) and diethylaluminium chloride (Al(C 2 H 5 ) 2 Cl) gave comparable activities for the production of polyethylene. Natta used crystalline α-TiCl 3 in combination with Al(C 2 H 5 ) 3 to produce first isotactic polypropylene . Usually Ziegler catalysts refer to titanium -based systems for conversions of ethylene and Ziegler–Natta catalysts refer to systems for conversions of propylene . Also, in

3657-469: The molecule and a half on the other. With a strength of 65 kcal/mol, the pi bond is significantly weaker than the sigma bond. Rotation about the carbon–carbon double bond is restricted because it incurs an energetic cost to break the alignment of the p orbitals on the two carbon atoms. Consequently cis or trans isomers interconvert so slowly that they can be freely handled at ambient conditions without isomerization. More complex alkenes may be named with

3726-417: The organic ligands are derivatives of cyclopentadienyl . In some complexes, the two cyclopentadiene (Cp) rings are linked with bridges, like −CH 2 −CH 2 − or >SiPh 2 . Depending on the type of their cyclopentadienyl ligands, for example by using an ansa -bridge , metallocene catalysts can produce either isotactic or syndiotactic polymers of propylene and other 1-alkenes. Ziegler–Natta catalysts of

3795-431: The photosensitiser, such as hydroxyl radicals , singlet oxygen or superoxide ion. Reactions of the excited sensitizer can involve electron or hydrogen transfer, usually with a reducing substrate (Type I reaction) or interaction with oxygen (Type II reaction). These various alternative processes and reactions can be controlled by choice of specific reaction conditions, leading to a wide range of products. A common example

3864-429: The physical properties of alkenes and alkanes are similar: they are colorless, nonpolar, and combustible. The physical state depends on molecular mass : like the corresponding saturated hydrocarbons, the simplest alkenes ( ethylene , propylene , and butene ) are gases at room temperature. Linear alkenes of approximately five to sixteen carbon atoms are liquids, and higher alkenes are waxy solids. The melting point of

3933-732: The position and conformation of the double bond. Alkenes are generally colorless non-polar compounds, somewhat similar to alkanes but more reactive. The first few members of the series are gases or liquids at room temperature. The simplest alkene, ethylene ( C 2 H 4 ) (or "ethene" in the IUPAC nomenclature ) is the organic compound produced on the largest scale industrially. Aromatic compounds are often drawn as cyclic alkenes, however their structure and properties are sufficiently distinct that they are not classified as alkenes or olefins. Hydrocarbons with two overlapping double bonds ( C=C=C ) are called allenes —the simplest such compound

4002-533: The position of its alkyl substituents (R) is called atactic. Both isotactic and syndiotactic polypropylene are crystalline, whereas atactic polypropylene, which can also be prepared with special Ziegler–Natta catalysts, is amorphous. The stereoregularity of the polymer is determined by the catalyst used to prepare it. The first and dominant class of titanium-based catalysts (and some vanadium -based catalysts) for alkene polymerization can be roughly subdivided into two subclasses: The overlap between these two subclasses

4071-499: The reaction is sensitive to conditions. This reaction and the ozonolysis can be used to determine the position of a double bond in an unknown alkene. The oxidation can be stopped at the vicinal diol rather than full cleavage of the alkene by using osmium tetroxide or other oxidants: This reaction is called dihydroxylation . In the presence of an appropriate photosensitiser , such as methylene blue and light, alkenes can undergo reaction with reactive oxygen species generated by

4140-447: The reaction medium. Traditionally such homogeneous catalysts were derived from metallocenes , but the structures of active catalysts have been significantly broadened to include nitrogen-based ligands. These catalysts are metallocenes together with a cocatalyst, typically MAO, −[O−Al(CH 3 )] n −. The idealized metallocene catalysts have the composition Cp 2 MCl 2 (M = Ti, Zr , Hf ) such as titanocene dichloride . Typically,

4209-420: The respiratory system. Titanium tetrachloride is a versatile reagent that forms diverse derivatives including those illustrated below. A characteristic reaction of TiCl 4 is its easy hydrolysis , signaled by the release of HCl vapors and titanium oxides and oxychlorides . Titanium tetrachloride has been used to create naval smokescreens , as the hydrochloric acid aerosol and titanium dioxide that

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4278-405: The solids also increases with increase in molecular mass. Alkenes generally have stronger smells than their corresponding alkanes. Ethylene has a sweet and musty odor. Strained alkenes, in particular, like norbornene and trans -cyclooctene are known to have strong, unpleasant odors, a fact consistent with the stronger π complexes they form with metal ions including copper. Below is a list of

4347-413: The symbols of its molecular formula ( TiCl 4 ). TiCl 4 is a dense, colourless liquid, although crude samples may be yellow or even red-brown. It is one of the rare transition metal halides that is a liquid at room temperature, VCl 4 being another example. This property reflects the fact that molecules of TiCl 4 weakly self-associate. Most metal chlorides are polymers , wherein

4416-410: The terminal position. Terminal alkenes are also known as α-olefins . The International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene , alkatriene , etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene , cycloalkadiene , etc. for cyclic ones; and "olefin" for

4485-413: The tetrahedral shape of the molecule. TiCl 4 adopts similar structures to TiBr 4 and TiI 4 ; the three compounds share many similarities. TiCl 4 and TiBr 4 react to give mixed halides TiCl 4− x Br x , where x = 0, 1, 2, 3, 4. Magnetic resonance measurements also indicate that halide exchange is also rapid between TiCl 4 and VCl 4 . TiCl 4

4554-436: The third class, non-metallocene catalysts, use a variety of complexes of various metals, ranging from scandium to lanthanoid and actinoid metals, and a large variety of ligands containing oxygen (O 2 ), nitrogen (N 2 ), phosphorus (P), and sulfur (S). The complexes are activated using MAO, as is done for metallocene catalysts. Most Ziegler–Natta catalysts and all the alkylaluminium cocatalysts are unstable in air, and

4623-418: The total volume of plastics, elastomers, and rubbers produced from alkenes with these and related (especially Phillips) catalysts worldwide exceeds 100 million tonnes. Together, these polymers represent the largest-volume commodity plastics as well as the largest-volume commodity chemicals in the world. In the early 1950s workers at Phillips Petroleum discovered that chromium catalysts are highly effective for

4692-662: The trichloride is a colored solid, being a coordination polymer , and is paramagnetic . When the reduction is conducted in THF solution, the Ti(III) product converts to the light-blue adduct TiCl 3 (THF) 3 . The organometallic chemistry of titanium typically starts from TiCl 4 . An important reaction involves sodium cyclopentadienyl to give titanocene dichloride , TiCl 2 (C 5 H 5 ) 2 . This compound and many of its derivatives are precursors to Ziegler–Natta catalysts . Tebbe's reagent , useful in organic chemistry,

4761-435: Was further extended to produce polypropylene . In the 1970s, magnesium chloride (MgCl 2 ) was discovered to greatly enhance the activity of the titanium-based catalysts. These catalysts were so active that the removal of unwanted amorphous polymer and residual titanium from the product (so-called deashing) was no longer necessary, enabling the commercialization of linear low-density polyethylene (LLDPE) resins and allowed

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