3 Methylbut 1 Ene Hbr

2-Methylbut-ii-Ene

Five- and Six-membered Fused Systems with Bridgehead (Ring Junction) Heteroatoms concluded: 6-6 Bicyclic with I or Two North or Other Heteroatoms; Polycyclic; Spirocyclic

Southward. Radl , in Comprehensive Heterocyclic Chemistry Iii, 2008

12.x.xiii.xi [1,2,four]Triazolo[1,two-c][1,3,4]oxadiazine

PTAD spontaneously reacts with various olefins to give the respective ene adducts, for instance, the reaction with 2-methylbut-2-ene gives a about quantitative yield of 645 <1980JOC3467>. When the reaction is run in acetone in the presence of various salts, for example, magnesium perchlorate, in add-on to 645 , triazolo[1,2-c]oxadiazine 646 is formed in 10–thirty% yield, depending on the reaction conditions ( Scheme 105 ) <1994T1821>.

Similar ene reactions of PTAD with chiral allylic alcohols 647 and their derivatives go along with complete regioselectivity and loftier diastereoselectivity, depending on the reaction temperature, to requite major threo- 648 and small-scale erythro-products 649 . The mixture is easily transformed past treatment with 2,2-dimethoxypropane in the presence of an acid catalyst to the respective bicyclic compounds 650 and 651 , respectively <1999JOC2194>. For compound 647 , R¹ = R² = Me, the relative configuration of these conformationally rigid derivatives studied past NOE spectroscopy conspicuously displays that the gem- 650 (threo) diastereomer is preferred in the ene reaction ( Scheme 106 ) <2002JA14403>.

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B978008044992001110X

Five-Membered Heterocycles

Vishnu Ji Ram , ... Ramendra Pratap , in The Chemistry of Heterocycles, 2019

Synthesis

1. The parent 1,ii-dithiolane has been obtained by oxidative cyclization of propane-one,iii-dithiol with iodine in the presence of 2-methylbut-2-ene or with potassium permanganate adsorbed on copper sulfate.

2. 1,2-Dithiolane-4,four-diyldimethanol has been prepared by the reaction of sodium tetrasulfide with ii,2-bis(bromomethyl)propane-1,3-diol in good yields.

3. three-Iodo-2-(iodomethyl) propionic acid on treatment with potassium salt of thioacetic acid and oxygen afforded 1,2-dithiolane-4-carboxylic acid.

Read total affiliate

URL:

https://www.sciencedirect.com/science/commodity/pii/B978008101033400005X

Five-membered Rings with One Heteroatom Together with Their Benzo and Other Carbocyclic-fused Derivatives

Ziyuan Li , ... Ning Jiao , in Comprehensive Heterocyclic Chemistry IV, 2022

3.02.2.3.3 N-Allylation with unactivated alkene

As discussed above, N-tert-prenylindole 91 could be prepared with activated prenyl carbonate xc. Even so, the N-tert -prenylation of indole can also exist achieved from unactivated two-methylbut-2-ene 106, probably through π-allyl palladium intermediate 107 (Scheme 22). ⁴³ This atom-economic dehydrogenative prenylation requires high loading of palladium catalyst, every bit well equally stoichiometric amounts of Ag^I and Cu^II salts equally external oxidants to close the catalytic cycle between Pd^Ii and Pd⁰. Meanwhile, C2-substitution on indole is detrimental to this reaction, which is probably due to steric hindrance.

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B978012409547214853X

Pyrolysis of Various Derivatives of Carboxylic Acids

Serban C. Moldoveanu , in Pyrolysis of Organic Molecules (Second Edition), 2019

Simple Lactones

β-Lactones are typically decomposed with CO₂ elimination and germination of an unsaturated compound. This reaction is shown beneath in general form:

(14.3.1)

For example, β-butyrolactone generates CO_two and propene. Similarly, α,α-dimethyl-β-butyrolactone (3,3,4-trimethyloxetan-2-1) generates CO₂ and 2-methylbut-ii-ene.

γ-Butyrolactone is the simplest γ-lactone. The compound is stable to heating and decomposes above 500°C by decarboxylation, generating CO₂ and propene [1]. A theoretical study on the mechanism of this reaction was reported in the literature [2]. The reaction probably takes place by a series of sequent steps, shown every bit follows:

(14.3.two)

A concerted mechanism was constitute to also be possible for γ-butyrolactone degradation because this mechanism is not significantly different regarding the activation energy, as compared with the consecutive path.

Tetrahydro-2H-pyran-2-one (δ-valerolactone) is a compound stable to heating upwardly to about 450°C. Its decomposition takes place with CO₂ emptying, but also with the formation of a number of fragment molecules.

Dicarboxylic acids can form esters with dihydroxy alcohols generating cyclic esters. These esters can exist considered lactones. One case is the ester of malonic acid with ethyleneglycol. The chemical compound decomposes with the formation of CO_ii, acetaldehyde, ethyl acetate, ethyleneglycol diacetate, and a big proportion of char. Both reactions of formation of ethyl acetate and ethyleneglycol diacetate involve more than complex transformations. The formation of ethyl acetate with the improver of external hydrogen is shown below:

(fourteen.iii.3)

Vinyl acetate was non isolated in the pyrolyzate of the ethyleneglycol ester of malonic acrid [3].

Pyrolysis of ethyleneglycol succinate takes place around 350°C and generates acetaldehyde, succinic acid anhydride, CO₂, and C₂H₄. The reactions in this process are shown below [3]:

(xiv.3.four)

Read total chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780444640000000147

Heterocycle-Fused Acridines

Paul West. Groundwater , Munawar Ali Munawar , in Advances in Heterocyclic Chemical science, 1997

2 Syntheses

Rutacridone 327 was synthesized for the commencement time by Mester et al. (81H77) by base of operations-catalyzed alkylation, with concomitant cyclization, of 1,3-dihydroxy-ten-methylacridin-9(10H)-ane 69 with one,four-dibromo-2-methylbut-2-ene. The linear isomer, isorutacridone 350, was also obtained every bit a byproduct (Scheme 66). A better yield of rutacridone 327 was obtained when A1_twoO₃ was used as the catalyst (90M829). Once over again, isorutacridone 350 was obtained as a past-product (Scheme 66).

Maier et al. have observed that microsomes (from Ruta graveolens prison cell cultures) catalyze the condensation of 1,3-dihydroxy-10-methylacridin-9(10H)-one 69 with isopentenyl pyrophosphate or dimethylallyl pyrophosphate, in the presence of NADPH and O₂, to produce rutacridone 327, and also that the reaction involved glycocitrine-II 265 equally an intermediate (90MI2; 93P691). A possible precursor 351 of rutacridone 327 has besides been isolated from a reaction of glycocitrine-II 265 with m-chloroperbenzoic acid (MCPBA) (Scheme 67) (93CPB383).

Selective hydroxylation of rutacridone 327 with SeO₂ in the presence of tBuOOH provided gravacridonol 331 (91LA299), and oxidation with KMnO_iv afforded rutagravin 339, isorutagravin 340, gravacridondiol 334, and dihydrohallacridone 353 [69CI(L)1809]. Dehydrogenation of dihydrohallacridone with DDQ produced hallacridone 347 [94JCR(S)157].

To confirm its structure, Reisch et al. have synthesized hallacridone 347 (Scheme 68) [89JCS(P1)1047]. Ullmann-amine coupling of ii-chlorobenzoic acid and 3,five-dimethoxyaniline gave an amine 354 that, on treatment with DMF-POCl₃, provided 4-formyl-1,3-dimethoxyacridin-9(10H)-ane 355. N-Methylation, O-demethylation, and subsequent condensation with 1-chloropropan-2-one in basic media gave hallacridone 347.

Takagi and Ueda have prepared a number of 4,5-dihydrofuro[two,3-c]acridines 358a–c from 4,5,6,seven-tetrahydrobenzofuran-four-ones 356 past condensing with isatin, anthranilic acid, and 2-aminophenylcarbonyl hydrochlorides 357 using a range of conditions (Scheme 69) (71CPB1218; 72CPB380, 72CPB2051). Dehydrogenation of iv,5-dihydrofuro[two,3-c]acridines 358 has as well been reported to requite the effluvious systems 359.

Coppola (84JHC1569) condensed N-methylisatoic anhydride 254 with the lithium enolate of 4,5,6,7-tetrahydrobenzofuran-4-one 356 (R = H) and obtained N-methylfuro[2,3-c]acridin-half dozen-one 361 subsequently dehydrogenation of the resultant iv,5-dihydrofuroacridone 360 (Scheme 70).

The method of Jayabalan and Shanmugan is novel in that it involves the construction of a ring between a quinoline and furan moieties to complete this skeleton (Scheme 71) (91ZN558).

Over again, we have used the strategy developed for the synthesis of pyrido[2,3-c]acridines to ready furo[two,3-c]acridines 362 (96TH1).

Read full affiliate

URL:

https://world wide web.sciencedirect.com/science/article/pii/S0065272508609307

Functional Group Exchange Reactions

Michael B. Smith , in Organic Synthesis (4th Edition), 2017

ten.2.ane Regioselectivity

Regioisomers have the same empirical formula, but groups or atoms are positioned at different carbon atoms. three-Methylhexanal and 4-methylhexanal are regioisomers, for example. A reaction that generates ane regioisomer as the major product can be regioselective, and if only one regioisomer is generated, and no others, the reaction is regiospecific. An instance is taken from i of the central transformations presented in Section 2.5.1 , addition to an alkene. The reaction of ii-methylbut-2-ene with HBr yields two-bromo-2-methylbutane equally the major product, a typical Markovnikov improver, with rather small amounts of 1-bromo-two-methylbutane, so the reaction is highly regioselective. This reaction proceeds by germination of the more stable carbocation, which reacts with the nucleophilic bromide ion. If the antiMarkovnikov bromide (i-bromo-2-methylbutane) is desired, a reaction with a dissimilar mechanistic pathway must be used. Reaction of the alkene with HBr and a peroxide gain by a radical machinery, giving 1-bromo-2-methylbutane, the anti-Markovnikov bromide (Department 2.5.1). ¹

Agreement which products are formed and the mechanism of how they are formed, is essential if one is to control which product is formed. Improver of HBr generates a carbocation, with the charge residing on the more than substituted carbon. The three alkyl substituents attached to the positive center provide more electronic stabilization to the p-orbital of the cation than is possible in the other possible intermediate, the principal carbocation. Reaction of the tertiary carbocation and the nucleophilic bromide ion generates 2-bromo-2-methylbutane as the major product.

When a peroxide is added to a mixture of Br₂ and an alkene, Br• is generated in situ (Sections 17.5.2 and 17.5.3) and this radical adds to the alkene to yield the more stable radical. The Br• reacts with the alkene, and the resulting product is an alkyl radical intermediate that reacts with more HBr to yield the anti-Markovnikov production, and more than bromine radical. If a reaction generates a carbocation, Markovnikov orientation is sure to upshot. If anti-Markovnikov addition is desired, the reaction must keep by a unlike reaction mechanism. The radical mechanism satisfies this requirement and if the reaction generates a radical, anti-Markovnikov orientation is preferred (Sections 2.5.1 and 17.five.2). ² ^, ³

Hydroboration of alkenes is some other regioselective reaction (see Section 9.2.2). Addition of borane to the alkene gives 2-methylbutan-1-ol, after oxidation of the intermediate alkylborane, a typical anti-Markovnikov addition product (Department 9.2.1). ⁴ The hydroboration-oxidation sequence is highly regioselective for generating the OH unit of measurement on the less substituted carbon cantlet of the alkene. The hydroboration reaction with alkenes to produce alkylboranes ⁴ gain past a 4-eye transition state rather than a cationic intermediate. The regiochemistry of the final alkylborane product is controlled by the nonbonded steric interactions of the groups attached to boron (in this instance sec-isoamyl from the disiamylborane) and the groups on the alkene. Oxidation with bones H_iiO₂ converts the borane to the anti-Markovnikov booze. With this alcohol in mitt, treatment with PBr₃ yields 1-bromo-two-methylbutane, the anti-Markovnikov bromide mentioned in a higher place. Once over again, understanding the primal machinery of the hydroboration reaction, allowed the preparation of the anti-Markovnikov booze from the alkene, followed by conversion to the bromide. It is clear from these examples, that a product with a certain regiochemistry can be synthesized by modifying the chemical reaction to follow a different mechanistic pathway, or past choosing a different chemic synthesis.

Read total affiliate

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B9780128007204000106

Additions to and Substitutions at C–C Π-Bonds

J.I. García , ... J.A. Mayoral , in Comprehensive Organic Synthesis (2nd Edition), 2014

four.20.2.10.2 Reaction of the metal–carbene circuitous

Iii alternative mechanisms (direct insertion, stepwise insertion, and metallacycle pathway) can exist considered for the cyclopropanation reaction of metal–carbene circuitous with an alkene.

4.20.ii.x.2.1 Directly insertion

In many cases, the metal–carbene complex reacts with the alkene through the simultaneous germination of both the new C single bond C bonds (e.m., meet Scheme fourteen). ^84,87 Equally such a step is typically very exothermic, and very early on transition states are common. ^84,88 Typical transition states show an approximately planar M double bond C versus olefin organization also equally an asynchronous approximation, according to theoretical calculations.

An electrophilic behavior of metal–carbene complexes has been inferred from Hammett studies on cyclopropanation reactions between a diazo compound (as ethyl diazoacetate 12 or methyl phenyldiazoacetate 39) and some sets of substituted styrenes by using a number of catalysts derived from Cu (forty, ⁸⁹ 41), ^ninety Rh (42, ⁹¹ 43), ⁹² Ru (44, ⁹³ 45), ⁹⁴ and Atomic number 26 (46). ⁹⁵

Instead, the nucleophilic behavior for metal–carbene complexes observed in the reactions of ethyl diazoacetate 12 with some substituted styrenes and using some Fe (47) or Co (48) catalysts ⁹⁶ can be attributed to a radical-like behavior of the complex.

The trans preference observed in many cyclopropanation reactions is commonly attributed to the occurrence of steric hindering betwixt the oxo functional group and the olefin alkyl substituent in the cis-transition state (Scheme 15). ⁹⁷

A comparison between the relative rates of several Rh₂(OAc)₄ 36-catalyzed cyclopropanation reactions of ethyl diazoacetate 12 for substituted olefins shows the reactivity order butyl vinyl ether xiii (8.6)>styrene 10 (3.5)>cyclohexene 49 (ii.five)>2,v-dimethylhexa-2,4-diene 50 (2.1)>ii-methylbut-two-ene 51 (ane.five), vinylacetate 52 (1.one), 1-hexene 52 (1.0). ⁹¹ Hence, an activating result alkoxy>aryl>acyloxy≈alkyl can be inferred for the alkene substituents in cyclopropanation reactions through direct insertion.

4.20.2.10.2.2 Stepwise insertion

Some cobalt–carbene complexes can undergo a stepwise diradicaloid reaction with olefins, according to theoretical (Scheme sixteen) ⁸⁶ and experimental studies. ⁹⁸ Thus, the porphyrin–cobalt circuitous 53 reacts with methyl diazoacetate 54 to yield the corresponding carbene complex 55, subsequently reacting with styrene 10 to yield the radical reaction intermediate 56, which regenerates the original catalyst 53 past loss of the corresponding cyclopropane (Scheme 16). As an interesting consequence of the diradicaloid reaction mechanism, electron-poor olefins can be efficiently cyclopropanated using Co(Two) catalysts.

4.20.2.ten.ii.iii Metallacycle pathway

A metallacycle mechanism tin can take place in some metallic-catalyzed cyclopropanation reactions. According to this pathway, the reaction betwixt the metal–carbene species and olefin takes place through a formal [2+2] cycloaddition leading to a metallacyclobutane, which subsequently undergoes a reductive elimination to yield the resulting cyclopropane.

As a representative instance of this mechanism, a Pd(0)-catalyzed reaction between styrene 10 and ethyl diazoacetate 12 tin can exist considered (Scheme 17). ⁹⁹ Thus, the catalyst precursor IPrPd(styrene)₂ 57 tin loss a styrene molecule through a reversible equilibrium to yield IPrPd(styrene) 58, which can react with ethyl diazoacetate 12 to generate a styrene-coordinated Pd ketocarbenoid, whereas Due north₂ is evolved. The styrene-coordinated Pd ketocarbenoid 59 can undergo an intramolecular [ii+2] cycloaddition to yield 1 or two regioisomeric palladacyclobutanes (60, 61). Reductive elimination of these metallacycles generates the resulting cyclopropanes as well as a Pd complex having a coordinative vacant (62), which tin can afterward react with a new styrene molecule to regenerate IPrPd(styrene) 58.

Some metals other than palladium can be involved in cyclopropanation reactions via metallacycles. Thus, a detailed theoretical study on a cyclopropanation reaction between styrene 10 and ethyl diazoacetate 12 catalyzed by a cationic Rh circuitous bearing a C,N-ligand (63) has shown the feasibility of the metallacycle pathway (Scheme 18), whereas the direct insertion mechanism could non operate. ¹⁰⁰

Preference for alternative mechanisms in cyclopropanation reactions involving metallic–carbene complexes can be contradistinct by geometrical constraints. Thus, according to theoretical calculations Co-catalyzed cyclopropanation reactions have shown that the concerted mechanism is favored for complexes showing a most coplanar surroundings, whereas the metallacycle pathway being preferred otherwise (see Scheme 19). ¹⁰¹ All the same, the most common scene is illustrated by a theoretical written report of an intermolecular Cu(I)-catalyzed reaction: both mechanisms beingness possible, direct insertion is slightly favored. ⁸⁴

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080977423004262

Nickel, Palladium, and Platinum

Yard. Brent Immature , in Comprehensive Organometallic Chemistry Two, 1995

9.ii.1.ii.(iii).(a) Alkene dissociation–displacement reactions

A kinetic evaluation (by ¹H NMR lineshape assay) of ethene exchange in both the Zeise anion and the dimer indicates that the reaction is first order in free alkene. Estimates for activation parameters for Pt₂Cl₄(η-C₂H_four)₂ (ΔH ^‡ = thirty ± four kJ mol⁻ⁱ, ΔS ^‡ = −23 ± 20 J mol^−one K⁻¹) and for [PtCl₃(η-C_iiH₄)]⁻ (ΔH ^‡ = 43 ± five kJ mol⁻ⁱ, ΔS = -43 ± 18 J mol⁻¹ K^−ane) sally to explicate the slower reaction of the mononuclear anion. At low temperature, trans-PtCl₂(η-C₂H_four)₂ is formed from Pt_iiCl₄(η-C_twoH₄)₂. These reactions are largely enthalpy controlled (in contrast with respective complexes with acac). ¹⁰² From kinetic analyses of the interaction of [PtCl_n(OH₂)_{4 − n}]^{(2 − due north)−} and ethene (n = 0–four), it emerges that, for trans-PtCl₂(OH₂)₂, parallel pathways give trans-PtCl_two(OH₂)(η-C₂H₄) and tran-[PtCl(OH₂)₂(η-C_twoH_iv)]⁺, by rates in the ratio 1:1.5. Alkenes, it is concluded, are relatively inefficient entering groups, comparable in reactivity with DMSO. ¹⁰³ Exchange of trans -ane,ii-dichloroethene (dee), 2,3-dimethylbut-2-ene (dmb) and 2-methylbut-2-ene (mbn) in optically active complexes trans-PtCl_iiL(η-(S)-mbn) is observable past following decay of round dichroism at ca 24 000 cm^−ane (L = py, 4-CN-py, 4-Cl-py, four-Me-py, 4-NH₂-py, aniline, 4-chloroaniline or 4-methylaniline). For L = py, the rate increases as the incoming alkene varies in the order dmb < dce < mbn, which is supported by both steric and electronic arguments. Rates for incoming dce, on the other paw, diminish as the +I effect of the para substituent on 50 increases. It is concluded that the σ-character of the Pt single bond Due north bail is an important contributor to the trans effect of L. ¹⁰⁴ Exchange of 3,three-dimethylbut-l-ene by styrene in the related system, trans-PtCl₂(py″)(η²-alkene), is catalysed by intramolecular germination of an O,Due north-chelate interaction (py″ = 2-(two-hydroxyethyl)-six-methylpyridine or 2-(2-hydroxypropyl)-6-methyl-pyridine). ¹⁰⁵ Dynamic NMR measurements lead to estimations of varying activation parameters (ΔH ^‡ = 54–75 kJ mol⁻¹ and ΔS ^‡ = −12–38 J mol⁻¹ K^−one) for alkene dissociation in a series of 4-substituted pyridine-N-oxide complexes, trans-PtCl₂(ONC₅H₄-4-Y)(ηⁱⁱ-alkene) (alkene = 4-methylbut-one-ene; Y = H, Me, CO₂Me, Cl or NO₂). ¹⁰⁶ Alkene dissociation also has a crucial role in the trans-cis isomerization of trans-PtX₂(PR₃)(η²-alkene) (Ten = Cl or Br; Fifty = PBu_iii or PMe₂Ph; alkene = ethene, propene or hept-1-ene). The trans isomers lose alkene in a photochemically influenced equilibrium with the corresponding dimer, from which the more stable cis isomers are formed. Exchange of complimentary alkene is faster in every case than isomerization, which is retarded by the presence of gratuitous alkene for X = Cl, simply slightly accelerated for X = Br. A dissociative path appears to predominate for chloro complexes, while an associative route is more important for bromo analogues. ¹⁰⁷

Equilibrium measurements for the reaction of [PtL_n(NCPh)]⁺ with ethene to yield respective ethene complexes [PtL_n(η-C₂H₄)]⁺ reveal equilibrium constants (1000) which vary in the order: PtL_northward = [Pt(PPh_iii){η-H₂CCH(Me)CH₂}]⁺ > [Pt(PPh_iii)Cp]⁺. For reactions of 4-substituted styrenes, iv-Y-C_half-dozenH₄CH double bond CH₂, with [Pt(PPh₃)_twoCp]⁺, the observed values of K increment with increasing electron-donating chapters of Y (Y = H, Me, OMe, NMe₂, Cl or NO₂). ¹⁰¹ [Pt(PPh_iii)(NCPh){η-H₂CCH(Me)CH_ii}]⁺ shows like reactivity with the same series of 4-substituted styrenes, H_iiC double bond CH-four-C_sixH₄Y. A linear correlation of K with Hammett parameters emerges, with ρ = −1.32, indicating the importance to bonding of σ-donation from the alkene to platinum. ⁶² A related examination of equilibration of the cis- and trans-but-2-ene analogues, [Pt(PPh₃)(η²-Z-C₄H₈){η-H₂CCMeCH_ii}]⁺ and [Pt(PPh₃)(η²-(E)-C₄H_viii){η-H₂CCMeCH₂}]⁺, for which K = 0.v, indicates a reversal of the normal stability trend (cis > trans) for metallic single bond alkene coordination. ⁶⁹ The ii-chloro- and ii-methylstyrene derivatives in the serial [Pt(PPh_three)(η-H₂C double bond CHC_sixH₄Y){η-H₂CCMeCH_two}]⁺ showroom lower solution stabilities than their iii- and 4-substituted analogues—as a effect, it is proposed, of in-aeroplane steric repulsion. A reversed stability order is observed in complexes where the coordinated alkene lies perpendicular to the coordination aeroplane (see Department 9.2.1.2(i)(c)). ⁶⁹ Stability trends in neutral complexes, PtCl(η-H₂C double bond CHR){η-H₂CC(Me)CH_ii} (R = Me, Et, Bz or iv-C₆H_ivY; Y = H, Me, Cl, OMe, NMe_two or NO₂) and cationic relatives, [Pt(PPh₃)(η-H_twoC double bond CHR){η-H₂CC(Me)CH₂}]ClO₄ (R = Me, Et or Bz), point greater electrophilic activation of a given alkene in cationic derivatives. ⁶⁶ For a related family of styrene complexes, Pt(C₆F_five)(η-H₂C double bond CHC₆H_fourY){η-H₂CC(Me)CH₂} (Y = H, 4-Me, 4-Cl, iv-OMe or three-NO₂), the platinum-alkene bail forcefulness is merely weakly dependent on the electronic backdrop of Y. For equilibration with the homologue where Y = H, Grand does not deviate appreciably from unity and, from a Hammett correlation, ρ = −0.38. ⁶⁸ Similarly, the solution stabilities of styrene complexes, PtCl₂(py)( η-H₂C double bond CHC₆H_fourY), exhibit higher stability for the more electron-altruistic alkenes and testify skilful correlation with the Hammett LFER, ρ = −0.82. These data are in accordance with the greater contribution from σ-donation than π-retrodonation to η-alkene single bond platinum bonding in these systems, ¹⁰⁸ and may be compared with those for [Pt(PPh₃)(η-H₂C double bond CH-4-C₆H₄Y){η-H_iiCCH(Me)CH₂}]⁺, where ρ = −1.32. ⁶²

An overview of applications of ii-dimensional NOESY NMR techniques includes an analysis of the fluxional behaviour of the styrene circuitous, [Pt(SnCl₃)(η-C₂H₃Ph){η-H_iiCC(Me)CH_ii}]. This suggests that SnCl₃ and styrene commutation processes are operating, but that in that location is no η^one, η^three-isomerization of the methallyl ligand. ¹⁰⁹

Extensive studies of alkene dissociation from PtXY(Northward single bond Due north′)(η²-alkene) illuminate the energetics of pentacoordination (relative to tetracoordination) for platinum(Two) systems of this type. For many such derivatives, alkene loss is a spontaneous and (effectively) irreversible procedure, while for numerous others—notably those where there is appreciable steric and/or electronic destabilization of the four-coordinate geometry—equilibria are appreciable. These results (including pK values) have been tabulated in a contempo survey of the topic. ⁷² There is prove that alkene dislocation in these species may sometimes follow a stepwise route, via preliminary loss of X⁻ from the inner coordination sphere to form planar tetracoordinate [PtY(N single bond North′)(η^two-alkene)]X, which, in turn, undergoes alkene displacement by X⁻ to give PtXY(NorthwardN′).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080465197000848

Alkenes oligomerization with resin catalysts

Bruno 1000. Antunes , ... Carlos M. Silva , in Fuel Processing Technology, 2015

iii.5 Isoamylene dimerization

Oligomerization studies have focused mainly on C₄ olefins regardless of the potential of C₅ olefin oligomerization to comply with new gasoline regulations [41,101]. In fact, C₅ olefins are undesired atmospheric ozone precursors responsible for more than than 90% of the ozone forming potential of gasoline [41,44,102]. Moreover, the increased demand of new depression-price octane boosters for gasoline blending draw the attention to diisoamylenes (C₁₀H₂₀) characterized by high octane numbers, around 96, and boiling points in the range of 420–430 K [101]. Diisoamylenes can be obtained by acrid catalyzed dimerization of C₅ olefins, namely the isoamylene isomers 2-methylbut-ane-ene and 2-methylbut-2-ene ( Fig. nine) [44]. Suitable catalysts include acrid-treated clays and strong acid ion commutation resins such equally Amberlyst-15 and -35 (Table i) [41,101,103].

Marchionna et al. [44] compared the performance of strong acid resins Amberlyst-15 and -35 (4.8 and five.2 meq H⁺ m^{− 1}, respectively) with medium acid capacity resins such as Amberlyst-XE586, a surface sulfonated resin, and Amberlyst-XN1010, a highly crosslinked resin (85 wt.% DVB [11]). Best results were obtained with resins containing the active sites mostly on the outer surface (Table ane) thus minimizing cracking and boosted oligomerization reactions (leading to trimers and tetramers) in understanding with the results by Yoon et al. [22] that reported better trimer selectivity with stronger acid resins. With Amberlyst-35 nether optimized weather the selectivity to dimers (C₁₀) reached 92–93% while trimer (C_xv) selectivity was below eight% [44].

Isoamylene dimerization is a highly exothermic reaction. Consequently feeding an booze with a depression alcohol/olefin molar ratio allows meliorate temperature command and, at the aforementioned time, increases dimer selectivity in detriment of trimers and tetramers, although ethers might exist formed as byproducts [2,41,69]. Since etherification is a much faster reaction only later reaching the ether equilibrium, isoamylene dimerization becomes the main reaction[41]. However, in the course of reaction isoamylene depletion promotes a continuous displacement of the ether equilibrium (i.eastward. ether decomposition). The polarity of the alcohol influences the swelling of the resin, reactivity of isoamylenes and the etherification equilibrium [41,104] while the presence of water in the booze decreases the resin catalytic activeness[41,103,105]. All things considered, the most polar alcohols are preferred selectivity enhancers [41,92].

Cruz et al. [41] tested several sulfonic acid resins (Table 6) for the liquid phase dimerization of isoamylene in the presence of methanol or ethanol (alcohol/olefin molar ratio 1:9) at 353 K and 1.9 MPa. No significant amounts of trimers, tetramers or slap-up products were detected. All-time results (higher conversion and selectivity) were obtained with the about acidic macroporous catalysts Amberlyst-35 and Purolite-CT275, in the presence of methanol (in contrast with previous reports where higher alcohols were preferred to increase dimer selectivity [2]). The gel-type resin Amberjet 1500H was the less effective [41] in agreement with previous oligomerization studies.

Tabular array vi. Conversion and selectivity results for isoamylene dimerization ^a [41].

Resin goad	Acidity (meq H⁺ g^{− 1})	Alcohol	10 _ISA ^b (%)	10 _OH ^c (%)	S _DI ^d (%) ^d
Amberlyst-15	4.81	MeOH	59.2	93.0	88.ii
Amberlyst-15	4.81	EtOH	39.8	80.9	67.8
Amberlyst-35	v.32	MeOH	60.seven	92.2	89.1
Amberlyst-35	v.32	EtOH	43.ane	79.three	71.ane
Amberjet-1500H	5.xx	MeOH	22.viii	88.7	32.iii
Amberjet-1500H	5.xx	EtOH	20.0	74.8	23.1
Purolite-CT175	4.98	MeOH	57.9	92.4	86.8
Purolite-CT175	4.98	EtOH	40.4	80.five	68.6
Purolite-CT275	5.xx	MeOH	lx.8	92.6	89.0
Purolite-CT275	5.xx	EtOH	42.1	81.8	70.0

a: Reaction conditions: liquid stage at 353 Thousand, 1.9 MPa and vii.two h of reaction.
b: Isoamylene conversion.
c: Alcohol conversion.
d: Selectivity towards diisoamylenes.

Cruz et al. [101] went on to written report the liquid phase dimerization of isoamylenes using Amberlyst-35 equally catalyst, in the temperature range of 333–373 Grand and testing several C_i to C₅ alcohols (x mol% of: methanol, ethanol, propan-i-ol, butan-1-ol, pentan-one-ol, propan-2-ol, butan-2-ol or t-butanol). Under those conditions trimers, tetramers, and not bad products were not detected. Selectivity for dimers was favored by high temperatures and was influenced by the presence and nature of the booze. All-time results were obtained with primary alcohols and, with the exception of methanol, dimer selectivity increased with the molecular weight of the alcohol (for case, with pentan-1-ol isoamylene conversion was fourscore% and selectivity to dimers was 95% at 373 K) [101]. With the secondary alcohols selectivity towards the dimers was much lower due to steric hindrances to ether formation, and with the tertiary alcohol (t-butanol) no reaction occurred [101]. Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were tested by plumbing equipment to experimental data (isoamylene liquid-phase dimerization catalyzed past Amberlyst-35, using a primary alcohol as selectivity enhancer) — the best fit was obtained considering negligible vacant sites on the catalyst surface and the rate limiting step is the surface reaction betwixt two adsorbed isoamylene molecules [106].

Granollers et al. [39] scrutinized various macroreticular ion exchange resin catalysts (namely Amberlyst-fifteen, -16, -35, -36, -46, -48, -70 and Purolite-CT175, -CT252, -CT275, -CT276, -MN500) for the liquid-stage oligomerization of isoamylenes (94 wt.% of 2-methylbut-two-ene and vi wt.% of 2-methylbut-one-ene) at 2 MPa and two different temperatures (343 and 383 G). For all experiments the most meaning products were diisoamylenes, triisoamylenes and some cracking products: oligomers higher than trimers were not detected. Although the tested catalysts differed in functionalization type and cantankerous-linking degree (Tabular array ane) at mild temperatures (343 K) no notable differences were observed in terms of selectivity with loftier dimer yields (up to 70%) and depression trimer yields (beneath 12%) for loftier levels of isoamylene conversion (ca. ninety%) [39]. At higher temperatures (383 K) dimer yields were lower (up to 60%) and trimer yields increased (upwards to xviii%) simply less than expected due to cracking reactions (the yield of not bad products reached xx%) [39].

Goad activeness and selectivity were both related to the parameter "superficial acrid density" (meq H⁺ m^{− two}), a term that lumps the acid chapters and the surface area of the resin and was considered a good predictor of macroreticular ion exchange resin reactivity (Table 1) [39]. Overall, the nearly active goad was the oversulfonated medium cross-linked resin Purolite-CT252 (TOF = 0.0637 mol (meq H⁺)^{− 1} s^{− 1} at 343 K and TOF = 0.1317 mol (meq H⁺)^{− 1} south^{− 1} at 383 Grand) whereas the least active catalyst was the conventional sulfonated medium cross-linked resin Amberlyst-16 (TOF 0.0023 mol (meq H⁺)^{− 1} s^{− i} at 343 One thousand and TOF 0.0027 mol (meq H⁺)^{− 1} south^{− ane} at 383 K) [39]. The low activity of resins Amberslyt-16 and -36 was associated to the polymer matrix collapsed structure that inhibits the admission to the internal agile sites [39].

Aiming the development of appropriate kinetic models for isoamylene oligomerization, Granollers et al. [39,107] ensured that the measured reaction rates were free of internal and external mass transfer resistances and checked the platonic behavior of the reaction mixture (i.e. reaction rates were expressed in terms of concentrations). In the absence of solvent the best model for dimerization was an Eley–Rideal (ER) machinery involving one active site (the rate limiting footstep being the surface reaction between one adsorbed isoamylene molecule and one costless isoamylene molecule) [39]. In the presence of north-hexane equally solvent and Amberlyst-15 as catalyst, the best kinetic models were based on LHHW–ER mechanisms accounting for isoamylene, dimer and due north-hexane in the adsorption term [100] and negligible concentration of vacant active sites [106,107]. Dimerization involves only one active site, i.due east. an adsorbed isoamylene molecule reacts with a not-adsorbed isoamylene molecule, with an activation energy of 37 ± two kJ mol^{− 1} [39,107]. Trimerization involves 3 agile sites i.e. the reaction occurs between adsorbed isoamylene (one active site) and diisoamylene (ii agile sites) molecules, with an activation energy of 89 ± iii kJ mol^{− ane} [39,107].

Read full commodity

URL:

https://www.sciencedirect.com/science/article/pii/S0378382015002003