Computational Study of Catalytic Urethane Formation

Polyurethanes (PUs) are widely used in different applications, and thus various synthetic procedures including one or more catalysts are applied to prepare them. For PU foams, the most important catalysts are nitrogen-containing compounds. Therefore, in this work, the catalytic effect of eight different nitrogen-containing catalysts on urethane formation will be examined. The reactions of phenyl isocyanate (PhNCO) and methanol without and in the presence of catalysts have been studied and discussed using the G3MP2BHandHLYP composite method. The solvent effects have also been considered by applying the SMD implicit solvent model. A general urethane formation mechanism has been proposed without and in the presence of the studied catalysts. The proton affinities (PA) were also examined. The barrier height of the reaction significantly decreased (∆E0 > 100 kJ/mol) in the presence of the studied catalysts, which proves the important effect they have on urethane formation. The achieved results can be applied in catalyst design and development in the near future.

Bonding and Reactivity of Gallium and Aluminium Coordination Complexes

<p>This thesis describes the synthesis, structures and reactivities of gallium and aluminium complexes supported by β-diketiminato ligands ([CR{C(R)N(R’)}₂]-, abbrev. [(BDIR’)]-). Chapter 1 gives a general introduction into the trends and properties that distinguish the heavier p-block elements from their lighter counterparts. An introduction into the theory of multiple bond formation, both homonuclear and heteronuclear, in the heavy p-block elements is provided and a summary of the sterically demanding ligands required to stabilise these complexes is introduced. The β-diketiminato ligand framework utilised in this study is introduced and the methods of generation of low valent gallium and aluminium complexes supported by the BDIDIPP ligand are discussed. Chapter 2 discusses the reactivity of the complex BDIDIPPGa with diazo- compounds in the quest to isolate a complex with a formal gallium-carbon double bond. BDIDIPPGa reacts with two equivalents of both trimethylsilyldiazomethane and diazofluorene, presumably through the target gallium-carbon double bond intermediate. No reaction is observed with di-tert-butyldiazomethane, while BDIDIPPGa catalyses the decomposition of diphenyldiazomethane into tetraphenylethene. Three new β-diketiminato gallium(I) complexes were synthesised: ArBDIDIPPGa, BDIAr*Ga and BDIAr’Ga. ArBDIDIPPGa also reacted with two equivalents of trimethylsilyldiazomethane, presumably through the target gallium-carbon double bond intermediate. BDIAr*Ga and BDIAr’Ga both inserted into the C-H bond of trimethylsilyldiazomethane to give BDIAr*Ga(H)C(N2)SiMe₃ and BDIAr’Ga(H)C(N2)SiMe₃ respectively. Upon addition of diazofluorene to BDIAr*Ga, one of the aromatic protons of the BDIAr* ligand was abstracted by the diazofluorene, resulting in coordination of one of the flanking phenyl groups to the gallium centre. Chapter 3 discusses an investigation into the formation of formal double bonds between aluminium and phosphorus, and gallium and phosphorus. The proposed ‘deprotonation/elimination’ method, reacting BDIDIPPM(PHAr)Cl (M = Al, Ga Ar = Ph, Mes) with nBuLi, resulted in the formation of intractable mixtures of products. Direct synthesis by the addition of MesPLi₂ to BDIDIPPMCl₂ (M = Al, Ga) resulted in the formation of BDIDIPPM(PHMes)Cl (M = Al, Ga). Changing the elimination product to TMS-Cl, through the synthesis of BDIDIPPM(P(TMS)Ph)Cl (M = Al, Ga), resulted in the synthesis of BDIDIPPAl(P(TMS)Ph)Cl, which showed no signs of elimination occurring upon heating to 110 °C. BDIDIPPGa(P(TMS)Ph)Cl could not be isolated, potentially as the complex was undergoing the desired elimination of TMS-Cl, but the resulting complex was decomposing. Changing the elimination product to ethane, through the synthesis of BDIDIPPAl(PHMes)Et, resulted in no sign of elimination occurring upon heating to 110 °C. Reduction of BDIDIPPMCl₂ (M = Al, Ga) in the presence of bistrimethylsilylacetylene, as part of the synthesis of BDIDIPPMLi₂ (M = Al, Ga) salts, was unsuccessful, as was the reaction of BDIDIPPGa with bistrimethylsilylacetylene. Reduction of MesPCl₂ with potassium metal in the presence of BDIDIPPGa resulted in an intractable mixture of products, reduction with magnesium resulted in the formation of (MesP)₃ and (MesP)₄. Addition of MesPH₂ to BDIDIPPGa resulted in the formation of BDIDIPPGa(H)P(H)Mes, which did not undergo H₂ elimination at 110 °C. The synthesis of BDIDIPPAl was unsuccessful as the product could not be isolated cleanly. The synthesis of ArBDIDIPPAl resulted in the intramolecular rearrangement of the ligand to give a five-membered aluminium containing ring. The synthesis of BDIAr*Al stalled at the formation of BDIAr*Al(Me)I due to the steric bulk of the ligand blocking the second substitution of iodine from occurring. Chapter 4 discusses the reactivity of the primary phosphanide complexes BDIDIPPAl(PHMes)Cl, BDIDIPPAl(PHMes)Et and BDIDIPPGa(H)P(H)Mes with phenyl acetylene, 4-nitro-phenyl isocyanate, phenyl isothiocyanate, dicyclohexyl carbodiimide, cyclohexene, benzophenone, benzaldehyde, selenium, sulfur, and methyl iodide. Reactivity was not observed for phenyl acetylene, dicyclohexyl carbodiimide or benzophenone with any of the phosphanides. Reactivity with the phosphanides was observed with cyclohexene, however rapid decomposition of the products occurred and they were unable to be identified. BDIDIPPAl(PHMes)Cl and BDIDIPPGa(H)P(H)Mes showed no reactivity with benzaldehyde, however, the ethyl ligand of BDIDIPPAl(PHMes)Et reacted with the aldehyde proton, eliminating ethane and substituting the PhC(O)- ligand onto the aluminium centre. Reactivity with the phosphanides was observed with both sulfur and selenium, however multiple different products were formed, none of which were successfully isolated. Reactivity between the phosphanides and methyl iodide was observed, with the P-M bond appearing to be cleaved and formation of a M-I bond occurring. 4-nitro-phenyl isocyanate and phenyl isothiocyanate underwent insertion reactions into the M-P bond, however only BDIDIPPAl(Cl)N(4-NO₂-Ph)C(O)P(H)Mes was able to be isolated and fully characterised. Finally, chapter 5 summarises the results of this research and provides an outlook at the future direction of this field of research.</p>

Bonding and Reactivity of Gallium and Aluminium Coordination Complexes

<p>This thesis describes the synthesis, structures and reactivities of gallium and aluminium complexes supported by β-diketiminato ligands ([CR{C(R)N(R’)}₂]-, abbrev. [(BDIR’)]-). Chapter 1 gives a general introduction into the trends and properties that distinguish the heavier p-block elements from their lighter counterparts. An introduction into the theory of multiple bond formation, both homonuclear and heteronuclear, in the heavy p-block elements is provided and a summary of the sterically demanding ligands required to stabilise these complexes is introduced. The β-diketiminato ligand framework utilised in this study is introduced and the methods of generation of low valent gallium and aluminium complexes supported by the BDIDIPP ligand are discussed. Chapter 2 discusses the reactivity of the complex BDIDIPPGa with diazo- compounds in the quest to isolate a complex with a formal gallium-carbon double bond. BDIDIPPGa reacts with two equivalents of both trimethylsilyldiazomethane and diazofluorene, presumably through the target gallium-carbon double bond intermediate. No reaction is observed with di-tert-butyldiazomethane, while BDIDIPPGa catalyses the decomposition of diphenyldiazomethane into tetraphenylethene. Three new β-diketiminato gallium(I) complexes were synthesised: ArBDIDIPPGa, BDIAr*Ga and BDIAr’Ga. ArBDIDIPPGa also reacted with two equivalents of trimethylsilyldiazomethane, presumably through the target gallium-carbon double bond intermediate. BDIAr*Ga and BDIAr’Ga both inserted into the C-H bond of trimethylsilyldiazomethane to give BDIAr*Ga(H)C(N2)SiMe₃ and BDIAr’Ga(H)C(N2)SiMe₃ respectively. Upon addition of diazofluorene to BDIAr*Ga, one of the aromatic protons of the BDIAr* ligand was abstracted by the diazofluorene, resulting in coordination of one of the flanking phenyl groups to the gallium centre. Chapter 3 discusses an investigation into the formation of formal double bonds between aluminium and phosphorus, and gallium and phosphorus. The proposed ‘deprotonation/elimination’ method, reacting BDIDIPPM(PHAr)Cl (M = Al, Ga Ar = Ph, Mes) with nBuLi, resulted in the formation of intractable mixtures of products. Direct synthesis by the addition of MesPLi₂ to BDIDIPPMCl₂ (M = Al, Ga) resulted in the formation of BDIDIPPM(PHMes)Cl (M = Al, Ga). Changing the elimination product to TMS-Cl, through the synthesis of BDIDIPPM(P(TMS)Ph)Cl (M = Al, Ga), resulted in the synthesis of BDIDIPPAl(P(TMS)Ph)Cl, which showed no signs of elimination occurring upon heating to 110 °C. BDIDIPPGa(P(TMS)Ph)Cl could not be isolated, potentially as the complex was undergoing the desired elimination of TMS-Cl, but the resulting complex was decomposing. Changing the elimination product to ethane, through the synthesis of BDIDIPPAl(PHMes)Et, resulted in no sign of elimination occurring upon heating to 110 °C. Reduction of BDIDIPPMCl₂ (M = Al, Ga) in the presence of bistrimethylsilylacetylene, as part of the synthesis of BDIDIPPMLi₂ (M = Al, Ga) salts, was unsuccessful, as was the reaction of BDIDIPPGa with bistrimethylsilylacetylene. Reduction of MesPCl₂ with potassium metal in the presence of BDIDIPPGa resulted in an intractable mixture of products, reduction with magnesium resulted in the formation of (MesP)₃ and (MesP)₄. Addition of MesPH₂ to BDIDIPPGa resulted in the formation of BDIDIPPGa(H)P(H)Mes, which did not undergo H₂ elimination at 110 °C. The synthesis of BDIDIPPAl was unsuccessful as the product could not be isolated cleanly. The synthesis of ArBDIDIPPAl resulted in the intramolecular rearrangement of the ligand to give a five-membered aluminium containing ring. The synthesis of BDIAr*Al stalled at the formation of BDIAr*Al(Me)I due to the steric bulk of the ligand blocking the second substitution of iodine from occurring. Chapter 4 discusses the reactivity of the primary phosphanide complexes BDIDIPPAl(PHMes)Cl, BDIDIPPAl(PHMes)Et and BDIDIPPGa(H)P(H)Mes with phenyl acetylene, 4-nitro-phenyl isocyanate, phenyl isothiocyanate, dicyclohexyl carbodiimide, cyclohexene, benzophenone, benzaldehyde, selenium, sulfur, and methyl iodide. Reactivity was not observed for phenyl acetylene, dicyclohexyl carbodiimide or benzophenone with any of the phosphanides. Reactivity with the phosphanides was observed with cyclohexene, however rapid decomposition of the products occurred and they were unable to be identified. BDIDIPPAl(PHMes)Cl and BDIDIPPGa(H)P(H)Mes showed no reactivity with benzaldehyde, however, the ethyl ligand of BDIDIPPAl(PHMes)Et reacted with the aldehyde proton, eliminating ethane and substituting the PhC(O)- ligand onto the aluminium centre. Reactivity with the phosphanides was observed with both sulfur and selenium, however multiple different products were formed, none of which were successfully isolated. Reactivity between the phosphanides and methyl iodide was observed, with the P-M bond appearing to be cleaved and formation of a M-I bond occurring. 4-nitro-phenyl isocyanate and phenyl isothiocyanate underwent insertion reactions into the M-P bond, however only BDIDIPPAl(Cl)N(4-NO₂-Ph)C(O)P(H)Mes was able to be isolated and fully characterised. Finally, chapter 5 summarises the results of this research and provides an outlook at the future direction of this field of research.</p>

Identification and Evaluation of Hazardous Pyrolysates in Bio-Based Rigid Polyurethane-Polyisocyanurate Foam Smoke

In this study, rigid polyurethane (PU) and polyisocyanurate (PIR) foam samples made from renewable material (tall oil fatty acid) based polyols were analyzed by pyrolysis gas chromatography mass spectrometry (Py-GC/MS) to obtain information about the full relative smoke content, with a focus on substance identification by their functional groups and hazardousness. The relative content of gaseous products produced during the thermal degradation was evaluated between the two samples, differenced by their assigned isocyanate (NCO) index value—150 and 300. The main thermal degradation components of the rigid PU-PIR foam were found to originate from the decomposition of isocyanate, primarily forming 4,4′-methylenedianiline, 3,3′-diaminodiphenylmethane, N-methylaniline, aniline, 4-benzylaniline and phenyl isocyanate. Hazard analysis revealed that the most common hazards were the hazards related to health: H315 (36%), H319 (28%), H335 (25%), and H302 (23%). The chemical compound with the highest relative content value—4,4′-methylenedianiline (45.3% for PU and 52.4% for PIR)—was identified to be a suspected carcinogen and mutagen. The focus of the study was identifying and evaluating the relative quantities of the produced gaseous products, examine their hazardousness, and provide information on the released thermal degradation products to form a renewable-source based rigid PU and PIR foam.

Derivatizing Reagents for Detection of Organic Compounds By HPLC

Derivatization is the process of chemically modifying a compound to develope a new compound which has properties that are suitable for analysis using HPLC. Derivatization improves the detectability of a target analyte by reaction with suitable derivatizing agent. Derivatization reactions are simple chemical modification of substance that make it compatible with the selected separation method or transforms substance with a low UV- absorption into highly sensitive product. Derivatization reactions in liquid chromatography modify the solutes adding a chomophore for easy UV detection or a fluorophore for sensitive fluorescent detection. The chemical structure of the compound remains same and just modifies the specific functional group for reacting compounds to derivative of deviating chemical and physical properties in order to make them detectable. Introduction of certain elements or groups through chemical derivatization may enhance the detector’s response helpful for the elucidation of structure of analytes. In conclusion, the present review describe various derivatization reagents for pre-column and post column derivatization process in HPLC by UV-visible and fluorescence detection are summarized along with reactions and some practical aspects. The commonly used derivatizing reagents in HPLC are 1-fluoro-2, 4-dinitrobenzene, ninhydrine, 4-N-N-dimethylaminoazobenzene-4’-sulfonyl chloride, benzoyl chloride, phenyl isocyanate for UV-visible detection and o-phthalaldehyde, fluorescamine, 1-dimethylaminonapthalene-5-sulfonyl chloride (DNS-Cl), 9-fluorenylmethyl chloroformate (Fmoc-Cl), benzofurans for Fluorescence detection.

5-Ethoxy-1-(4-methoxyphenyl)-5-methyl-3-phenylimidazolidine-2,4-dione

The title compound is a hydantoin derivative that has been synthesized through a three-component reaction of ethyl pyruvate, p-anisidine and phenyl isocyanate. This paper provides a comprehensive spectral dataset for the title compound, including 1H and 13C{1H} NMR, IR, HRMS, and X-ray crystallography analyses. A tentative mechanism comprising two complementary pathways is provided based on additional experiments with the preformed intermediates.

Kinetically Equivalent Functionality and Reactivity of Commonly Used Biocompatible Polyurethane Crosslinking Agents

In this paper, the kinetics of the reaction of phenyl isocyanate with crosslinking agents such as sucrose, sorbitol, and glycerol are reported. Crosslinking agents were used in high molar excess to isocyanate to obtain pseudo-first-order rate dependencies, and the reaction products were separated by high-performance liquid chromatography and detected by UV spectroscopy and mass spectrometry. It was found that the glycerol’s primary hydroxyl groups were approximately four times reactive than the secondary ones. However, in the case of sorbitol, the two primary OH groups were found to be the most reactive, and the reactivity of hydroxyl groups decreased in the order of kOH(6)(8.43) > kOH(1)(6.91) > kOH(5)(1.19) > kOH(2)(0.98) > kOH(3)(0.93) > kOH(4)(0.64), where the numbers in the subscript and in the brackets denote the position of OH groups and the pseudo-first-order rate constants, respectively. The Atomic Polar Tenzor (APT) charges of OH groups and dipole moments of monosubstituted sorbitol derivatives calculated by density functional theory (DFT) also confirmed the experimental results. On the other hand, the reactions of phenyl isocyanate with crosslinking agents were also performed using high excess isocyanate in order to determine the number of OH-groups participating effectively in the crosslinking process. However, due to the huge number of derivatives likely formed in these latter reactions, a simplified reaction scheme was introduced to describe the resulting product versus reaction time distributions detected by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). Based on the results, the kinetically equivalent functionality (fk) of each crosslinking agent was determined and found to be 2.26, 2.6, and 2.96 for glycerol, sorbitol, and sucrose, respectively.

The Effect of Surface Treatment with Isocyanate and Aromatic Carbodiimide of Thermally Expanded Vermiculite Used as a Functional Filler for Polylactide-Based Composites

In this work, thermally expanded vermiculite (TE-VMT) was surface modified and used as a filler for composites with a polylactide (PLA) matrix. Modification of vermiculite was realized by simultaneous ball milling with the presence of two PLA chain extenders, aromatic carbodiimide (KI), and 4,4’-methylenebis(phenyl isocyanate) (MDI). In addition to analyzing the particle size of the filler subjected to processing, the efficiency of mechanochemical modification was evaluated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The composites of PLA with three vermiculite types were prepared by melt mixing and subjected to mechanical, thermomechanical, thermal, and structural evaluation. The structure of composites containing a constant amount of the filler (20 wt%) was assessed using FTIR spectroscopy and SEM analysis supplemented by evaluating the final injection-molded samples’ physicochemical properties. Mechanical behavior of the composites was assessed by static tensile test and impact strength hardness measurements. Heat deflection temperature (HDT) test and dynamic thermomechanical analysis (DMTA) were applied to evaluate the influence of the filler addition and its functionalization on thermomechanical properties of PLA-based composites. Thermal properties were assessed by differential scanning calorimetry (DSC), pyrolysis combustion flow calorimetry (PCFC), and thermogravimetric analysis (TGA). The use of filler-reactive chain extenders (CE) made it possible to change the vermiculite structure and obtain an improvement in interfacial adhesion and more favorable filler dispersions in the matrix. This translated into an improvement in impact strength and an increase in thermo-mechanical stability and heat release capacity of composites containing modified vermiculites.