Aroylcarboxylic Acid Corrosion Inhibitors

1. Field of the Invention

This invention relates to the use of special aroylcarboxylic acids as corrosion inhibitors in aqueous systems.

2. Statement of the Related Art

Corrosion prevention in aqueous systems is a major problem in industrial processes involving susceptible metals, such as copper, zinc or aluminium. Previously, the use of corrosion inhibitors, for example in cleaning preparations, cooling lubricants, hydraulic fluids or cooling waters, has often resulted in a number of practical problems. Foam suppression, solubility, and stability in hard water, are all important to the usefulness of corrosion inhibitors. In addition, the toxicity and degradability of corrosion inhibitors and also their shelf life are crucial factors.

Long chain aliphatic sulfonamidocarboxylic acids and arylsulfonamidocarboxylic acids have recently been proposed as corrosion inhibitors. However, they are only effective against corrosion when used in high concentrations and, in many cases, do not satisfy the performance standards mentioned above.

It has now been found that excellent results are obtained when alkali and/or ammonium salts of at least one compound corresponding to the following Formula ##STR2## in which R.sub.1 and R.sub.2 independently are hydrogen or a C.sub.1-6 -alkyl radical and R.sub.3 is CH.dbd.CH, (CH.sub.2).sub.2 or (CH.sub.2).sub.3, are used as corrosion inhibitors in aqueous systems.

Compounds corresponding to Formula I in which R.sub.1 is a C.sub.3-4 -alkyl radical and R.sub.2 is hydrogen are particularly suitable.

It has also been found that, in addition to alkali salts such as sodium or potassium salts, ammonium salts with organic bases are preferred, such as ammonia, mono-, di- or trialkanolamines. Diethanolamine (DEA) is particularly preferred.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".

The corrosion inhibitors according to the invention may be used either on their own or in admixture in the form of aqueous solutions, dispersions or emulsions optionally with compatible non-interactive adjuvants and/or carriers. They should be used in any corrosion inhibitive effective amount. They are extremely effective even in low concentrations. Thus, it has been found that, in some cases, an adequate effect is obtained with as little as 0.5 kg/m.sup.3. Accordingly, the inventive corrosion inhibitors are used in quantities of from 0.5 to 10 kg/m.sup.3 preferably in quantities of from 1 to 10 kg/m.sup.3 and most preferably 1 to 5 kg per m.sup.3 of aqueous system. In addition, the inhibitors used produce little foam and are highly stable to the hardness of water.

The aroylcarboxylic acids are produced by methods known per se. For example, they may be obtained by the Friedel-Crafts acylation of alkylbenzenes with corresponding cyclic anhydrides. The production of the aroylcarboxylic acids and their salts does not form any part of the present invention.

The corrosion inhibiting properties were determined by measuring the degree of erosion using the following procedure:

Three carefully pretreated and weighed test strips (unalloyed steel, 80.times.15.times.1 mm) were suspended in a 1 liter vessel containing 800 ml of test water, 50 ml of buffer solution and a predetermined quantity of the inhibitor to be tested and left therein for 3 hours at room temperature/80 r.p.m.

The corrosion inhibition value S, based on a blank test specimen, was calculated from the weight loss. ##EQU1##

The test water used as the corrosive medium was prepared in accordance with Deutsche Industrienorm (DIN) 51,360/2 and buffered with ammonia/ammonium chloride.

The results obtained by comparison with the prior art benzene sulfonamidocaproic acid are shown in Table 4 below. Tables 1 to 3 correlate Examples A to T with Formula I. The bases mentioned were used to neutralize the aroylcarboxylic acids.

For the purposes of this invention, the minimum acceptable S value is 85%, with 90% being preferred and 95% being most preferred. A careful analysis of the test results indicates that it is difficult to find a statistically significant difference between the variables (R.sub.1, R.sub.2, R.sub.3, and base). However, the S values for Examples A to H are particularly good, and these Examples are distinguished by R.sub.2 being H and R.sub.3 being CH.dbd.CH, R.sub.1 and the base being variable.