DEP0052564DA - Heating bath fluids - Google Patents

Description

There are relatively very few organic and inorganic compounds that have a boiling point within the range of 300-450 °, i.e. that can be used as heating bath fluids within the specified temperature range. This number is significantly reduced if such high-boiling compounds are intended to be liquid at room temperature and, on the other hand, are not allowed to undergo any thermal decomposition at their boiling point at atmospheric pressure.

It has now been found that heating bath liquids consisting of a high-boiling and a lower-boiling <illegible> component are outstandingly suitable for use in heating baths with reflux.

Such components are the following:

Diethyl phthalate, boiling point 298-9 °

Ethyl acetate "77.1 °

Phenanthrene "340 °

Chlorobenzene "132 °

Diphenylamine "302 °

Diisobutylamine "139 °

Benzoic Anhydride "360 °

Diisopropyl ketone "123.7 °

Orthosilicic acid-o-cresol-

ester "435-8 °

Orthocresol "191 °

Orthosilicic acid-o-

xylenol ester "460 °

Orthoxylenol "203 °

Tetralin "204-6 °

Orthosilicic acid-m-

xylenol ester "453-7 °

1,2,3,5-tetramethylbenzene "195-7 °

Depending on the mixing ratios, certain constant temperatures of the heating bath can be set with such mixtures, as can be seen, for example, from the following list:

250 ccm orthosilicic acid bath temperature ° C

m-cresol ester + ccm m-cresol approx.

- 425.5

1,423.5

2 421

3 404

4,384

5 360

6 336

8 325

10 316

15 298

20 286

30 274

40 265

50 254

Correspondingly, the course with other components of the mixture and when using inert high-boiling organic compounds as additional components, e.g. tetralin bp 204-206 °, 1,2,3,5-tetramethylbenzene bp 195-197 °, with a low solidification point of the additional component still being favorable affects the condition of the liquid bath.

The information given above is somewhat different depending on the dimensional ratios used in the apparatus, although for a certain apparatus the bath temperature of the refluxing liquid can be precisely regulated by setting the mixing ratio of the components. The extent to which the apparatus arrangement causes certain fluctuations in the adjustability of the bath temperature of the refluxing liquid mixture is evident from the following considerations. Let the same volume of liquid e.g. of orthosilicic acid-m-cresol ester with a certain addition of about m-cresol be contained in apparatus a and in b, whereby a smaller space is available for the evaporating component in apparatus a than in apparatus b. This results in a higher bath temperature for b than for a. However, by adding a certain amount of m-cresol, the bath temperature of b can easily be adjusted to that of a. The reason for the different bath temperatures in the two apparatuses lies in the different size of the gas space above the liquid up to the cooler, ie with a less m-cresol can be present in the gas space than with b, and therefore a smaller amount is present in the mixture with a withdrawn of cresol on heating under reflux than in b. Since the bath temperature rises when more cresol is withdrawn, the higher bath temperature must also be present at b. As can be seen from this, only the proportion of m-cresol that remains in the liquid when it boils is decisive for the exact setting of the bath temperature. The same applies to the other components of the mixture, the other additional component being decisive instead of cresol.

When using a certain orthosilicic acid ester as an additional component, it is advisable to use the phenol that is contained in the ester, since when using a different phenol the bath temperature can change somewhat over time, as a result of transesterification, such as: until a final equilibrium is established, while the addition of the same ester-containing phenol and the addition of an inert high-boiling component ensures the immediate, precise setting of the bath temperature.

A mixture of orthosilicic acid crude cresol ester with crude cresol, for example, is particularly advantageous for the production of such high-boiling bath liquids with a precisely adjustable bath temperature when heating under reflux.

Even if these aromatic silicic acid esters are less sensitive to water at boiling point than the corresponding aliphatic esters (whereby the ester is split into SiO (sub) 2 and alcohol more or less quickly), it is useful to achieve an even longer shelf life to connect the reflux condenser to a dry system, in order to avoid any entry, including traces of water.

The principle on which the invention is based is that when such a mixture is heated, the low-boiling component partially evaporates and is returned to the bath liquid in the circuit through the reflux condenser, creating an equilibrium between the low-boiling component present in the vapor space and that in the bath adjusts existing proportion of low-boiling component.

The mixing ratio of low-boiling to high-boiling liquid in this state of equilibrium is decisive for setting the constant bath temperature. The bath temperature can be set to a certain level by changing the ratio of the mixture components. These liquids also offer the advantage, in reactions that require a uniform temperature range, to dissipate the heat of reaction that may be released via the heat of evaporation of the low-boiling component. On the other hand, by constantly distilling off the low-boiling component, the bath temperature can be regulated from a lower temperature level to a higher one in appropriate times by then adjusting the decrease in the distillate.

Claims (2)

1.) Heating bath liquid consisting of high-boiling and lower-boiling components for use in heating baths with reflux cooling. 2. Heating bath fluids consisting of mixtures of orthosilicic acid phenol esters and phenols according to claim 1.