DE1240845B - Process for the production of dimethylketene by pyrolysis of isobutyric anhydride - Google Patents

Description

DEU

PATENT OFFICE

EDITORIAL

German class; 12 ο -19/03

Number: 1240845

File number: E 26326IV b / 12 ο

Filing date: February 1, 1964

Opened on: May 24, 1967

■ 'Μ

In the German patent 1182 652 a process for the preparation of dialkyl ketenes is the formula

: c = c = o

R '

where R and R 'are lower alkyl groups, by thermal cleavage of carboxylic acid anhydrides described, which is characterized in that dialkyl acetic anhydrides of the formula

: ch — c:

R '
Rs

—C

in which R and R 'have the above meaning, ^{are pyrolyzed at temperatures from 400 to 700 °} C. in the absence of catalyst.

Although this process is quite general for the production of dialkyl ketenes, and indeed has proven extremely effective on an industrial scale, but are occasionally used in the production of Dimethylketene from isobutyric anhydride encountered certain difficulties, which are their cause have that the z. B. in a cold condenser or in a dry ice trap at temperatures of 0 ° C or below trapped dimethylketene at such low temperatures with air to one can convert extremely sensitive and highly explosive, solid peroxide.

The formation of explosive by-products in the by pyrolysis or cracking of isobutyric anhydride Dimethylketene obtained can be switched off in the simplest manner by a process for the production of dimethylketene by pyrolysis of isobutyric anhydride according to patent 1182 652, which is characterized in that the high-boiling fractions of the pyrolysis products in one Vacuum of 1 to 100 mm and a temperature of at least 20 ° C of the dimethyl ketene formed separates and the dimethyl ketene is collected at a temperature of at least 20 ° C.

The required temperature control can be achieved in that the pyrolysis products process for the production of Dimethy lketen
by pyrolysis of isobutyric acid anhydride

Addendum to the patent: 1182 652

Applicant:

Eastman Kodak Company,

Rochester, N. Y. (V. St. A.)

Representative:

Dr.-Ing. W. Wolff, H. Bartels

and Dr.-Ing. J. Brandes, patent attorneys,

Munich 22, Thierschstr. 8th

Named as inventor:

Theodore Edward Stanin,

Vada Leeroy Brown Jr., Kingsport, Tenn.

(V. St. A.)

Claimed priority:

V. St. v. America 4 February 1963 (255 958)

from the bottom of the furnace in which they are formed, through an insulated connecting pipe or conduit, to a heat exchanger separator having a jacket, which is supplied with steam or a steam-water mixture of suitable pressure and temperature through the jacket the device is kept at a temperature of at least 20 ° C and preferably at least 30 ° C. After all high-boiling fractions present in vapor form, such as isobutyric acid and unreacted isobutyric anhydride, have condensed in the heat exchanger separating device, i.e. removed from the product stream, the volatile dimethylketene can be passed from there through a line that is kept at a constant temperature by a suitable temperature control medium is held by at least 20 ⁰ C, preferably about 70 ⁰ C or higher (such as. for example, 70 to 160 ° C). The temperature control takes place in that steam or another temperature-regulating medium is sent through a line that runs parallel to or in

709 587/568

3 4 f _Z \

Windings around another line and in front of the heat exchanger separating device 23

preferably is in direct contact therewith, d. H. with enclosing coat 26 was passed and this

the line is soldered or welded, through which left by a line 27, at or above min-

the vaporous or liquid material, its at least 20 ° C and preferably at above at least

Temperature is to be controlled, is kept ^{as 5 30 0 C.} The mixture of gaseous di-

in the present case dimethylketene. Thus, methylketene and liquid and vaporized, do not graze

according to the invention all surfaces between converted isobutyric anhydride and isobutter

the pyrolysis furnace and the point where the dimethyl acid flowed from the bottom up through the heat

keten is collected at or above a minimum exchanger separator 23 and was therein

temperature of 20 ° C and preferably stripped from the gaseous dimethylketene above about 10,

Maintained 30 ° C. which through a line 28 to the vacuum pump

The invention is further achieved by the drawing 10, while the vaporous isobutter

explained. It shows acid anhydride and isobutyric acid in the heat

F j g. 1 condenses a pyrolysis device downstream of the inventive exchanger separating device 23 and

application in a semi-schematic representation, 15 together with the, if necessary, from the start

Fig. 2 is a diagram showing the gas volume present liquid isobutyric anhydride, etc.

can be read that when the detonation of the same from the bottom through a line 26a, the

Converting a certain amount of dimethylketene contained a valve built into a storage container

rivers formed with air at different temperatures. Inert gas, such as B. the one originally used for flushing

peroxide-containing material, from which clearly 20 len of the system nitrogen used, was developed by

shows how crucial or critical it is that the container 29 via a valve and a line 30

Temperature of the dimethyl ketene product at 2O ⁰ C in the dimethyl ketene product stream through the

or to hold on to. Line 28 to pump 10 strönite, returned.

The following examples are intended to illustrate the process of the dimethylketene flowing through line 28

Illustrate the invention in more detail. 25 current was at at least 20 ° C, preferably at

a higher temperature of 70 to 160 ° C, including

Example 1 th by adding steam of about 6.3 atmospheres via the pressure regulator 31 through a line 34, which the di-

A device such as is arranged adjacent in FIG. 1, semi-schematic, methylketene discharge line 28

is shown table, was by means of a vacuum 30 and, as in Fi g. 1 shown spirally around the

pump 10 was led around to a pressure of 1 to 100 mm vacuum pump 10,

evacuated. The pressure was measured with a manometer 11 Before and after the pressure regulator 31 there were manometers

measured. Every hour 750 ml isabutyric acid meters 32 or 33 were connected to the steam line.

anhydride from a reservoir 12, which has a sen that indicated the vapor pressure. In the one from the

a valved line 12a with nitrogen 35 device leaking dimethyl ketene was not

was kept under a pressure of 1.05 kg / cra ² , explosive peroxide present,
through a filter 13, a rotameter 14 and a

Line 15 in an electrically heatable pyrolysis example 2
oven 16 fed. The level of isobutyric acid

arihydrids in the container 12 were measured by a measuring 40 In this example, essentially the same

tube 16 a made of glass displayed. All parts of the device worked rather like in example 5 of the

which are described with the starting material and the main patent, with the exception of each

Pyrolysis product came into contact, consisted of that a device as in F ig. 1 shown,

stainless steel. The oven was 71.1 cm long and used and the temperature was below the oven at

had a diameter of 26.7 mm. 45 about or above at least 20 ° C, d. H. about about

The top of the furnace 16 was maintained at room temperature and the air out of the pre-electric Resistance 17 to 600 ° C internal temperature removed by evacuation to 1 to 100 mm heated up. The temperature in the upper part of the was. The isobutyric anhydride was by a Oven 16 could be removed from the storage container through a sliding thermal filter and a rotameter element 18 or optionally by several in 50 fed to the pyrolysis tube in a metered amount. To the different heights inside the furnace - Pyrolysenete heated by two electric ovens Thermocouples are eaten. The lower pipe was preceded by a preheating spiral in which the Part of the furnace 16 could be preheated by means of a cooling jacket before it was passed through the anhydride 19, which a suitable cooling medium, such as. B. cracking zone was performed. The hot vapors were water, Was fed via a line 20 to 55 in the lower part of the furnace to a temperature Chilled to a temperature of about 35 to 70 ° C is quenched from about 60 to 70 ° C. The one weden. The cooling medium left the jacket 19 over a considerable amount of dimethyl ketene in addition to high-boiling ones a line 21. Components such as tsobutyric acid and not

Gaseous dimethylketene and partially condensed isobutyric anhydride containing, from

Sated, unreacted isobutyric anhydride 60 lower part of the furnace at a temperature of

as well as the iso- about 60 to 70 ⁰ C formed in the pyrolysis reaction pyrolysis products exiting

Butyric acid were fed from the bottom of the oven when they were jacketed to one

a temperature of about 35 ° C and led heat exchanger separator. the

through a line 22 in the lower part of the heat-temperature of the heat exchanger separator

exchanger separator 23 out. The temperature was reduced to less than 65 with a steam-water mixture.

temperature in the heat exchanger separator at least 20 ° C, preferably 30 ° C, held. The high-

23 was produced by a steam-water mixture made up of boiling constituents such as isobutyric acid and not

the mixer 24 through a line 25 to and through reacted isobutyric anhydride, were in the

Device condenses and then fed to a storage container, while the dimethylketene was drawn off by means of a vacuum pump through a line which was heated ^{to 70 to 160 ° C.}

As in Example 1 , the formation of explosive peroxides in the system and in the dimethylketene emerging from the system was also completely avoided here.

The following examples show how important it is that the temperature in the device parts does not fall below about 20 ° C, preferably not below about 30 ° C, downstream of the cracking chamber.

Example 3

An injection syringe became a brass bowl 6.4 mm in diameter given so much dimethylketene that the ground was just covered. The dimethylketene reacted with the oxygen in the air to form a white film. The bowl was then attached to the flask of a device such as that used for investigating detonability used by connections. Here, as is known, a weight of a certain size is derived from a dropped at a certain height onto a sample of the compound to be tested. The volume of the Gases released by the reaction triggered by the impact of the weight on the connection, is a measure of the explosiveness or detonability of the compound in question. In the present case a weight of 6.8 kg was dropped onto the sample over a distance of 76.2 cm, what a Equivalent to work of about 5.2 mkg. The gases resulting from the detonation of the sample moved the Piston of the test device in a calibrated gas burette. The change in volume that occurred was measured. During the investigation, the brass bowl was placed on an aluminum bowl Temperature was kept at the temperatures required for the tests by baths.

The volumes of gas obtained for each temperature at five or six detonations were averaged. The average values thus found were shown as the ordinate in the volume-temperature diagram in the drawing, while the corresponding test temperatures are plotted as the abscissa became. In addition, a blank value (empty bowl) was determined for five bowls on the test device.

The gas volumes (mean values) measured at different temperatures are shown in the table below compiled:

At temperatures at which large amounts of peroxide are formed, the amount of gas is proportionate high. At higher temperatures the amount of gas is smaller. The amount of out of these Peroxides obtained at temperatures above 0 ° C gas decreases rapidly with increasing temperature and approaches that of the blind test above 30 ° C. Accordingly, at around room temperature and considerably less detonable ίο peroxides formed than at lower temperatures. Of the The boiling point of the dimethyl ketene is 34 ° C, which is why the test temperature does not exceed 33.5 ° C could be.

Example 4

A thermometer was inserted into a test tube containing a 5% solution of dimethylketene in Contained isobutyl acetate. The tube and contents were cooled to 5 ° C. The thermometer was then taken from the

so tube pulled out. Under the action of air A white polymer-like film formed on the liquid film adhering to the thermometer, the was touched with a glass rod after 2 minutes and detonated weakly. The one on the thermometer The temperature read directly before the detonation was about 1.0 ° C. The small amount of peroxide-containing Polymer did not smash the thermometer or the glass rod.

Example 5

temperature Gas volume ⁰ C ml -70 0.90 + 0 0.84 -10 0.52 20th 0.34 33.5 0.23 Blank test (20 ° C) 0.14

The gas volume is a function of the amount of detonable dimethyl ketene peroxide present.

In a flask that contained dimethyl ketene and on which a cold finger was placed, which with a Mixture of acetone and dry ice was filled, air was left. The temperature of the cooling bath was - 70 ° C. The cold finger was with a dimethylketene flag covered. A white polymer-like film formed on contact with air on the cold finger. This film detonated with such force that the glass finger shattered and the flask containing the dimethylketene was practically destroyed.

Example 6

In a solution of 1.7 g in 18 ml of di-2-äthylhexylphthalat dissolved dimethylketene was introduced a weak stream of air at 25 ⁰ C. The highest peroxide concentration achieved was 0.075 milliequivalent. When the sample was tested in the test device mentioned earlier, no detonation could be caused at 62.2 mkg.

Claims (2)

Patent claims: 1. A process for the preparation of dimethyl ketene by pyrolysis of isobutyric anhydride according to patent 1182652, characterized in that the high-boiling fractions of the pyrolysis products are separated from the dimethyl ketene formed at a reduced pressure of 1 to 100 mm and a temperature of at least 20 ° C and the dimethyl ketene at at a temperature of at least 20 ° C.
2. The method according to claim 1, characterized in that at temperatures of at least 30 ° C. 1 sheet of drawings