Joback’s method

Heat Capacity. The multiple property estimation methods for constant pressure ideal-gas heat capacities cover a broad range of organic compounds (188,216,217). Joback s method (188) is the easiest to use however, usage of all these methods has been recommended only over the range 280—1100 K (7). An accurate method for ideal-gas heat capacities (constant pressure), limited to hydrocarbons, has been presented (218) that involves a fit of seven variables, and includes steric, ring, branching, alkene, and even allene corrections. 

Joback s method is an improved version of earlier methods, and attempts to estimate many properties of all the organic compounds. Table 5.13 shows the recommended Joback coefficients to build up the boiling and melting points of a compound, according to the formula... 

Similar methods that involve more elaborate equations have been proposed by Thinh (1971), Yoneda (1979), and Joback (1984). Thinh s method is of limited use because of its restriction to hydrocarbons, whereas Joback s method is more general and therefore more useful in organic synthesis. A few other methods have also been proposed (e.g., Kothari and Doraiswamy, 1964) that are easy to use, but are less accurate. 

Note that Joback s method estimates the values only at 298 K, and hence is not useful as a general method for estimating A//n- This is also true of the method based on the heat of combustion calculated from Equation 3.28 in kJ/ mol (Cardozo, 1986) ... 

Joback s method with methylcyclohexane as reference substance (Figure 3.3) The normal boiling point for methylcyclohexane isTb = 373.95K. 

Joback s method is generally accurate for the formation properties. It is very accurate for organic compounds and easier to use than other methods such as Constantinou Gani s, Benson s, and so forth(Poling et al., 2001). That s why it is convenient to encode and build expert system. 

Partial molar volumes and the isothermal compressibility can be calculated from an equation of state. Unfortunately, these equations require properties of the components, such as critical temperature, critical pressure and the acentric factor. These properties are not known for the benzophenone triplet and the transition state. However, they can be estimated very roughly using standard techniques such as Joback s modification of Lyderson s method for Tc and Pc and the standard method for the acentric factor (Reid et al., 1987). We calculated the values for the benzophenone triplet assuming a structure similar to ground state benzophenone. The transition state was considered to be a benzophenone/isopropanol complex. The values used are shown in Table 1. 

Devotta, S., and V. R. Pendyala, Modified Joback Group Contribution Method for Normal Boiling Point of Aliphatic Halogenated Compounds. Ind. Eng. Chem. Res., 1992 31, 2042-2046. 

Suppose that the compound s phase at 25°C was of interest. This question would have been answered correctly for all three compounds, although the quantitative estimation of Tm is not very precise. Suppose that the compound s phase at 20°C was of interest. This question would have been answered correctly for cyclopropyl methyl ether and 1,2-cyclopentenophenanthrene, but not for anethol. The magnitude of the interval (7 m)estimated - Timerestl can serve as a confidence measure for binary decision of the foregoing type. If (7 m)estimated interestI is lower than 50°C, a decision as to whether a compound is fluid or solid at interest should not be made based on Tm estimated using the method of Joback and Reid. 

One of the most important contributions to this field was provided by Stein and Brown [117], who extended Joback and Reid s group contribution method [122], The authors calculated 85 group contributions and used a nonlinear quadratic equation to correctly predict BP at high temperatures. The authors calculated MAE = 15.5 K for a set of 4426 compounds and predicted another independent set of 6584 compounds with MAE = 20.4 K. The method was further parameterized by Syracuse Research Inc using 6484 compounds and was used in the MPBPVP program [101]. 

Estimation Methods for Critical and Other Properties 257 Table 6.9-1 Joback Group Contribution.s to Pure Component Propertie.s... 

Norma/Bo//wg Point—Free ng Point. One method s deviation for boiling and freezing point data is reported to be less than 2 K for 80% of a 600 compound set and less than 5 K for an additional 18% (201). However, this method is limited to organic compounds having only one functional group and a short base group such as methji, vinji, and phenji. In contrast, the Joback method (188) has much wider apphcabflity and a reported average error of 12.9 K. 

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