Symfony process run throws exception - executing on command line works

PHP Snippet 1:

$command = '';
$count = 0;
foreach ($executionProcess as $value) {
    if($count != 0) {
        // parameters quoted:
        $command .= " ";
        $command .= '"' .$value .'"';
    }
    else {
        // exe
        $command .= $value;
    }
    $count++;
}
$command .= " > nul";
\Log::info('Command: ' .$command);
$descriptorspec = array(
    0 => array("pipe", "r"),  
    1 => array("pipe", "w"), 
    2 => array("file", env('PROCOPENERRORLOG') ."procOpenErrors.log", "a")
);
$cwd = str_replace("\\", "/", base_path()) .'/app/Classes/Bericht/Tex/Working';
$env = null;
$process = proc_open($command, $descriptorspec, $pipes, $cwd, $env);
if (is_resource($process)) {
    fwrite($pipes[0], '<?php print_r($_ENV); ?>');
    fclose($pipes[0]);
    echo stream_get_contents($pipes[1]);
    fclose($pipes[1]);
    $return_value = proc_close($process);
}