A simple method to evaluate, correlate and predict boiling and flash points of alkynes
Flash point and boiling point are the important physical property of the flammable liquids, and are important parameters to evaluate their combustion behavior. Goal: Flash point and boiling point data for compounds, arranged in a to the known flash point of similar chemical compounds or (ii) on a correlation to. The flash point of a volatile material is the lowest temperature at which vapours of the material will ignite, when given an ignition source. The flash point is.
If the compound's normal boiling point is higher, then that compound can exist as a liquid or solid at that given temperature at atmospheric external pressure, and will so exist in equilibrium with its vapor if volatile if its vapors are contained. If a compound's vapors are not contained, then some volatile compounds can eventually evaporate away in spite of their higher boiling points.
Boiling points of alkanesalkenesethershalogenoalkanesaldehydesketonesalcohols and carboxylic acids as a function of molar mass In general, compounds with ionic bonds have high normal boiling points, if they do not decompose before reaching such high temperatures. Many metals have high boiling points, but not all. Very generally—with other factors being equal—in compounds with covalently bonded moleculesas the size of the molecule or molecular mass increases, the normal boiling point increases.
When the molecular size becomes that of a macromoleculepolymeror otherwise very large, the compound often decomposes at high temperature before the boiling point is reached. Another factor that affects the normal boiling point of a compound is the polarity of its molecules. As the polarity of a compound's molecules increases, its normal boiling point increases, other factors being equal.
Flash point - Wikipedia
Closely related is the ability of a molecule to form hydrogen bonds in the liquid statewhich makes it harder for molecules to leave the liquid state and thus increases the normal boiling point of the compound. Simple carboxylic acids dimerize by forming hydrogen bonds between molecules. A minor factor affecting boiling points is the shape of a molecule. Although these values for Ai are empirical, they are chemically reasonable. They can be rationalized as the net effect of the loss of dispersion resulting from the removal of four hydrogen atoms from the corresponding alkane and the increase in intermolecular attraction made possible by the greater linearity of a structure with a carbon-carbon triple bond.
Only three carbons are necessarily collinear in a 1-alkyne, so the overall effect is a slight decrease in intermolecular attraction.
A 2-alkyne has four collinear carbon atoms at one end of the chain, so intermolecular attraction is much greater than in the corresponding alkane. A 3-alkyne also has four collinear carbon atoms, but now there are non-collinear segments at each end of that four-carbon segment.
As a result, the total increase in intermolecular attraction is less than for a 2-alkyne, so the Ai value for a 3-alkyne is less positive than that of a 2-alkyne.
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- Flash Point, Fire Point, Boiling Point & Auto Ignition Point Relat
The non-collinear segments are even longer for a 4- or higher alkyne, so the Ai value for a 4-alkyne is smaller still. An even better correlation between literature and predicted values can be obtained by use of separate parameters for 4-alkynes and 5- or higher alkynes.
We judged the improvement insufficient to justify addition of another parameter, however. As an example of the application of equation 3, consider the calculation of YBP for 2-methyloctyne. This is a 3-alkyne, so the Ai value is 0. There is one methyl substituent on C2, so M is 1.
The longest chain has eight carbon atoms, and the total number of carbons in the molecule is nine. The YBP value calculated from equation 1 is The YBP values of the other alkynes were calculated from equation 3 in the same way, and these YBP values were then used to predict TB values with equation 4.
The correlation presented here is more accurate than any alkyne boiling point method previously reported. A group contribution method for non-electrolytes, which was based on counts of molecular fragments and a steric factor plus consideration of group interactions, gave an AAD of 3. It gave an AAD of 6. Additionally, the correlation reported here is based directly on structure counts, so it does not require specialized software for implementation.Definition of Boiling point,flash point Melting Point,freezing point
Not only does the method presented here allow the prediction of boiling points for compounds that have not yet been characterized, but it also can be used to evaluate literature boiling point data.
As shown in Figure 3the reported boiling point of 2-tetradecyne For this reason, we had concluded that the reported TB value of 2-tetradecyne is likely to be in error and excluded this compound from the data set. That assessment is validated by the YBP values shown in Figure 3.
The flash point TFP of a liquid is the lowest temperature at which the mixture of vapor and air above the substance can be ignited. For this reason, flash points are the standard measure of the fire hazard associated with the storage, transport, and use of flammable compounds. Experimental flash points are often unavailable for alkynes, however, and we could locate experimental TFP values for only about half of the alkynes in our data set.
Recently we introduced the flash point number, NFP, as a new measure of the flammability of organic liquids. The relationship reported between flash points and NFP values is shown in equation 5.
For monoalkynes, T is 1, and both D and B are 0, so equation 6 reduces to equation 7. We used equation 7 and YBP values predicted with equation 3 to calculate the NFP values of the compounds in our data set.
Then we used those NFP values in equation 5 to predict their flash points. Equation 5 was developed with a data set of linear and branched alkanes having boiling points of K or lower and flash points of K or less. A similar pattern was observed in the current study, so the limit of applicability of equation 5 seems to be TB values below K.
Further work will be necessary to determine a more accurate correlation of NFP and TFP values for higher boiling alkynes. The R2 of the correlation was 0. This result compares favorably with those of other methods for predicting hydrocarbon flash points from structure, which give AADs of K.
Conclusions The boiling point prediction method presented here is not only very easy to apply to acyclic alkynes, but it is also more accurate than previous methods. Comparison of reported alkyne boiling points with those predicted using equation 4 offers a simple means to identify literature TB values that should be redetermined.