Kinetic study of stilbene synthesis with benzyltriphenylphosphonium bromide as phase transfer catalyst

Abstract

A kinetic study of the Wittig reaction for synthesizing stilbene is carried out by reacting benzaldehyde (C₆H₅CHO) with benzyltri‐phenylphosphonium bromide (BTPPB) in the NaOH(aq)/CH₂Cl₂(org) two‐phase reaction system. The rate of reaction depends on the agitation speed, the temperature and the concentrations of C₆H₅CHO, BTPPB, and NaOH. When the agitation speed is low, the reaction is highly affected by interface diffusion. The reactant rate constant, based on the S_N 2 substitution mechanism and the activation energy are also determined. It is found that the activation energy obtained from the present study (E_a =11.97 kcal/mole) is less than that of the previously documented data (E_a =12.984 kcal/mole) in which benzyltriphenylphosphonium chloride (BTPPC) was used as a phase transfer catalyst.     

Effects of solvents and molecular weights of polyethylene glycols on the allylation of phenoxide

Abstract

In the present study, the synthesis of allyl phenyl ether by reacting sodium phenoxide and allyl bromide using PEGs as phase transfer catalysts either in a homogeneous phase or in a two‐phase reaction was studied. The reaction in a homogeneous phase was carried out using EtOH as the solvent and the reaction in a two‐phase was carried out using aprotic solvents, such as dichloromethane, chlorobenzene, ethyl ether, cyclohexane and n‐decane. In the homogeneous phase reaction, the effects of the molecular weights of PEGs on the initial reaction rate were investigated in detail. The aprotic properties of the PEGs were used to explain the variation in experimental results due to the use of different molecular weight PEGs. The reactivity of the reaction, which was influenced by the organic solvents in a two‐phase reaction, was also examined. The effects of the polarity of the solvents, the solubility of sodium phenoxide in the organic phase and the viscosity of the solution on the two‐phase reaction were employed to explain the experimental results satisfactorily.     

High CO2/CH4 and C2 Hydrocarbons/CH4 Selectivity in a Chemically Robust Porous Coordination Polymer

A new porous coordination polymer, ([La(BTB)H₂O]·solvent ( 1 ?guest)), is synthesized. Gas adsorption, ideal adsorbed solution theory (IAST) and breakthrough experiments of it exhibits high CH₄ separation capability toward CO₂ and C2 hydrocarbons at 273 K. In addition, this also shows good water and chemical stability, in particular, it is stable at pH = 14 at 100 °C, which is unprecedented for carboxylate‐based porous coordination polymers. Furthermore, the effective adsorption site for separation is revealed by using an in situ diffuse reflectance IR fourier transform (DRIFT) spectra study.     

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

ABSTRACT

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps     

Degradation of ozone-refractory organic phosphates in wastewater by ozone and ozone/hydrogen peroxide (peroxone): the role of ozone consumption by dissolved organic matter

Ozonation is very effective in eliminating micropollutants that react fast with ozone (k > 10(3) M(-1) s(-1)), but there are also ozone-refractory (k < 10 M(-1) s(-1)) micropollutants such as X-ray contrast media, organic phosphates, and others. Yet, they are degraded upon ozonation to some extent, and this is due to (?)OH radicals generated in the reaction of ozone with organic matter in wastewater (DOM, determined as DOC). The elimination of tri-n-butyl phosphate (TnBP) and tris-2-chloroisopropyl phosphate (TCPP), added to wastewater in trace amounts, was studied as a function of the ozone dose and found to follow first-order kinetics. TnBP and TCPP concentrations are halved at ozone to DOC ratios of ～0.25 and ～1.0, respectively. The (?)OH rate constant of TCPP was estimated at (7 ± 2) × 10(8) M(-1) s(-1) by pulse radiolysis. Addition of 1 mg H(2)O(2)/L for increasing the (?)OH yield had very little effect. This is due to the low rate of reaction of H(2)O(2) with ozone at wastewater conditions (pH 8) that competes unfavorably with the reaction of ozone with wastewater DOC. Simulations based on the reported (No?the et al., ES&T 2009, 43, 5990-5995) (?)OH yield (13%) and (?)OH scavenger capacity of wastewater (3.2 × 10(4) (mgC/L)(-1) s(-1)) confirm the experimental data. Based on a typically applied molar ratio of ozone and H(2)O(2) of 2, the contribution of H(2)O(2) addition on the (?)OH yield is shown to become important only at high ozone doses.     

The use of legal action in New York City to ensure treatment of tuberculosis

BACKGROUND AND METHODS: After an increase in the number of cases of tuberculosis, New York City passed regulations to address the problem of nonadherence to treatment regimens. The commissioner of health can issue orders compelling a person to be examined for tuberculosis, to complete treatment, to receive treatment under direct observation, or to be detained for treatment. On the basis of a review of patients' records, we evaluated the use of these legal actions between April 1993 and April 1995. RESULTS: Among more than 8000 patients with tuberculosis, regulatory orders were issued for less than 4 percent. Among patients with a variety of social problems, only a minority required regulatory intervention: 10 percent of those with injection-drug use, 16 percent of those with alcohol abuse, 17 percent of those who were homeless, 29 percent of those who used "crack" cocaine, and 38 percent of those with a history of incarceration. A total of 150 patients were ordered to undergo directly observed therapy, 139 patients to be detained during therapy, 12 patients to be examined for tuberculosis, and 3 patients to complete treatment. These 304 patients had a median of three prior hospitalizations related to tuberculosis and one episode of leaving the hospital against medical advice. Repeatedly noncompliant patients and those who left the hospital against medical advice were more likely than others to be detained. The median length of detention was 3 weeks for infectious patients and 28 weeks for noninfectious patients. As compared with patients ordered to receive directly observed therapy, the patients who were detained remained infectious longer, had left hospitals against medical advice more often, and were less likely to accept directly observed therapy voluntarily. Altogether, excluding those who died or moved, 96 percent of the patients completed treatment, and 2 percent continued to receive treatment for multidrug-resistant tuberculosis. CONCLUSIONS: For most patients with tuberculosis, even those with severe social problems, completion of treatment can usually be achieved without regulatory intervention. Patients were detained on the basis of their history of tuberculosis, rather than on the basis of their social characteristics, and the less restrictive measure of mandatory directly observed therapy was often effective.     

Improving urban classification through fuzzy supervised classification and spectral mixture analysis

In this study, a fuzzy‐spectral mixture analysis (fuzzy‐SMA) model was developed to achieve land use/land cover fractions in urban areas with a moderate resolution remote sensing image. Differed from traditional fuzzy classification methods, in our fuzzy‐SMA model, two compulsory statistical measurements (i.e. fuzzy mean and fuzzy covariance) were derived from training samples through spectral mixture analysis (SMA), and then subsequently applied in the fuzzy supervised classification. Classification performances were evaluated between the ‘estimated’ landscape class fractions from our method and the ‘actual’ fractions generated from IKONOS data through manual interpretation with heads‐up digitizing option. Among all the sub‐pixel classification methods, fuzzy‐SMA performed the best with the smallest total_MAE (MAE, mean absolute error) (0.18) and the largest Kappa (77.33%). The classification results indicate that a combination of SMA and fuzzy logic theory is capable of identifying urban landscapes at sub‐pixel level.     

Buckling of a Weakened Column

The buckling problem of a column weakened at an interior location is studied for the first time. The weakness is modeled by a rotationally restrained junction. Exact buckling load values are obtained for the weakened column with various end conditions. Depending on the end conditions of the column, the buckling loads show sensitivity (and insensitivity) to junction location and rotational stiffness. The optimum location of the junction could be at the midpoint, at the ends, or somewhere in between.